Highlights

• The most ruthless anime villains often serve as powerful foils to the heroes, pushing them to become better versions of themselves.
• Fans looking for anime stories with ruthless villains may have trouble sifting through the options to find the "perfect" fit.
• From characters like Rau Le Creuset to Yami Marik, anime's most ruthless villains come in various forms, each with their own sinister motives.

When it comes to media like anime that has a flair for impressive aesthetics and compelling storytelling, villains grab as much attention as heroes. After all, the most ruthless and evil anime villains motivate protagonists to become better versions of themselves. While they almost always fail in their grand designs, some are ruthless enough to earn a spot among the most horrifying characters in their respective franchises or anime as a whole.

Fans looking for anime stories with ruthless villains might find it difficult to sift through all the options to find their “perfect” fit. Which villains, with their brutality, mercilessness, and twisted philosophies, end up becoming perfect fits for the “ruthless” description?

Updated on April 12, 2024, by Rhenn Taguiam: With villains like My Hero Academia’s All For One, Jujutsu Kaisen’s Sukuna, and even Demon Slayer’s Muzan Kibutsuji earning the wrath of viewers due to their status as their respective anime’s antagonists, fans of the anime genre might be wondering how exactly they would fare against the rest of anime history’s merciless villains. While other anime villains have become notable for their goals and motivations, other antagonists have become infamous simply for being too evil. Aside from the aforementioned three antagonists, anime’s most ruthless villains also include a Char archetype from a Gundam series, as well as the broken malicious persona in a children’s card game.

25 Rau Le Creuset (Gundam SEED)

Self-Proclaimed Judge Of Humanity's Extinction

Almost all series within the Gundam franchise since the original Mobile Suit Gundam have had a “Char Archetype,” a role Rau Le Creuset takes as the lead antagonist of Gundam SEED. It’s already implied that he has some connection with Earth Federation’s Mu La Flaga, as their interactions are often preceded by harsh headaches. As the superior officer of Athrun Zala, Rau has proven numerous times his capability as a strategist. He is often found steps ahead of the Archangel’s crew, predicting where they might go and how to best engage them.

Rau is even more brutal as a Mobile Suit pilot, as his spatial awareness allows him to predict his opponent’s moves and even force them to reveal their hand through feints. Unlike other pilots in the series, Rau has shown capabilities of adapting to various suits and even managed to overwhelm a SEED-enhanced Kira Yamato and his Freedom Gundam during their fight.

Claim To Infamy: Became A Genocidal Villain

As a Char Archetype, Rau is presented as a charismatic individual who’s always calm and reasonable even when facing his opponents. However, he becomes akin to the level of other ruthless anime villains when confronted in the final episodes of the series. It’s revealed that Rau is a mere clone of Al Da Flaga, a wealthy politician who believed his son Mu was “nothing” after being “polluted” by the DNA of his mother. Being a clone crippled the psyche of Rau, leading him to install himself as mankind’s executioner. Seeing humanity as a mere “world of endless desires,” Rau wanted to use the world’s nuclear arsenal to eliminate all humans - Naturals and Coordinators, alike - including himself.

24 Shinobu Sensui (Yu Yu Hakusho)

Wanted Demons To Wreak Havoc On Earth For Humanity's Own Evil

Fans of Yu Yu Hakusho remember the arrogant yet noble Yusuke Urameshi and his signature Spirit Gun, while those with an eye for villains will remember Shinobu Sensui. Koenma’s spirit detective prior to Yusuke, Shinobu quit his job and went into hiding prior to resurfacing with a plot to destroy the world. This was tragic, considering Shinobu had a strong spiritual perception. To him, humans are purer than demons, and it’s his job to exterminate demons to stop them from threatening humans.

However, Shinobu witnessed an event where humans lavishly tortured demons for his amusement. With his moral compass broken, Shinobu unconsciously developed multiple personalities to salvage what was left of his mental state. With demons being vermin and humans being unworthy of saving in his eyes, Shinobu will stop at nothing to see the two species wipe each other out.

Claim To Infamy: The Feast Of Human Vices

Instead of having an act that cemented his ruthlessness, Shinobu Sensui had an instance that pushed him past the brink of sanity. The character’s initial black-and-white thought of demons being evil and humans being good allowed him to kill demons with sheer mercilessness, seeing humans relish in the torture of demons in the ritualistic Feast of Human Vices turned Sensui’s life upside down. Unable to comprehend the reality that humans may be just as monstrous as demons, Sensui killed everyone present in the ritual and blamed it on Kazuya, one of the many personalities he developed to cope with his broken mentality. Disillusioned by humanity, Sensui’s pursuit of breaking the Kekkai Barrier to unleash demonic havoc on Earth felt like a punishment he had to dole out to the evil people he was mistakenly protecting.

23 Muzan Kibutsuji (Demon Slayer)

The Smallest Slight Is Reason Enough For Him To Kill

As most demons fought by the Demon Slayer Corps of Demon Slayer tend to be aggressive and disorganized, it came as quite a surprise when their leader turned out to be the rather fashionable and calculating Muzan Kibutsuji. Throughout the series, this Demon King was revealed to be not only the leader of the Demon Slayer Corps’ sworn enemies, but he was also their very creator.

When his mission to cure his sickness transformed him into a powerful and immortal demon, Muzan set his sights on “true” immortality by conquering his weakness towards sunlight. This obsession with his goals reflected outward into everything around him, with the villain never settling for anything less. As such, Muzan is known to be extremely flamboyant with a penchant for perfection, whose ego and megalomania will have him kill anyone who dares even turn an eye on him in the wrong way.

Claim To Infamy: Kills On A Whim

It’s not within Muzan’s incredible control over bodily matter and his extraordinary strength as a demon where his ruthlessness lies. Rather, it’s how his manipulative and cunning persona hides a sickeningly cowardly person. While Muzan can easily kill anyone on a whim, the Demon King avoids direct conflict with powerful foes - even in his final conflict with the Demon Slayers. This quality makes his scheming especially more annoying, as much of the pain suffered by characters in the series is due to Muzan’s machinations. Muzan turned Tamayo into a demon outside her knowledge, making her kill her family. He was also aware of the Kamado family’s connection with the Sun Breathing Style, thus making it his business to kill them.

22 Light Yagami (Death Note)

Murdering Criminals Is Just For His New World

When Light Yagami receives the Death Note, he soon realizes that writing anyone’s name in it will kill that person. Thus begins Death Note and Light’s quest to kill criminals himself, ushering in the birth of a perfect and lawless world as Kira. However, Light’s journey toward godhood is continuously hindered by the authorities, particularly L, who proves to be his nemesis. Soon enough, Light will stop at nothing to achieve his goals.

Despite Light being the “protagonist” of Death Note, he’s truly its main villain. To Light, being Kira and using the Death Note to kill criminals has become a daily routine. He manipulates his way into the favor of others to transform them into his allies or disciples and then discards them when they’re of no use.

Claim To Infamy: The Thought Of Killing Sayu

When unsavory forces kidnap Light’s sister Sayu to force their father, Kira Task Force leader Soichiro Yagami, to hand over the Death Note, the series protagonist finds himself in an alliance with L’s successor Near. Unfortunately for the Death Note protagonist, Near tells him his rival and fellow protege, Mello, may have been responsible. Concerned about the lies he has to keep up with the Death Note’s rules, Light considers killing Sayu to ensure Mello doesn’t get his hands on the Death Note. While he doesn’t push through with it, just the thought that he would be willing to sacrifice his family for his goals makes him all the more heartless.

21 Hisoka Morow (Hunter X Hunter)

Would Stop At Nothing To Meet A Strong Opponent

Fans of Hunter X Hunter might be amused at the idea of the world hiring Hunters to conduct a wide variety of tasks, with the likes of Hisoka Morow existing far beyond the reach of the regular professional. Practically a criminal and a fugitive, Hisoka exists only to find the strongest fighters to do battle for his amusement. It doesn’t help that his Transmutation Nen is perfectly suited for combat, with Hisoka using his signature Bungee Gum to create sheets, strings, and constructs that have the elasticity of rubber and durability to even catch and ricochet projectiles back to attackers on top of his absurdly strong physique.

Such is the inherent selfishness of Hisoka that he only pursues his objectives for combat and pleasure. He will willingly switch sides and betray his allies if it means being amused. Moreover, his cunning and manipulative side allows Hisoka to pit factions against each other with nary a care in the world. Had it not been for protagonist Gon’s potential as a Hunter, Hisoka would have already killed him at the beginning of the series.

Claim To Infamy: What It Takes To Get A Good Fight

Hisoka’s acts of indiscriminate murder had become somewhat of a “trademark” in the Hunter X Hunter anime, especially to satiate his obsession for a good fight. Much of this is seen in his fascination with Chrollo Lucifer, the leader of the Phantom Troupe. On top of selling out the Phantom Troupe to protagonist Kurapika just to fight Chrollo, Hisoka refused to fight the then-powerless leader. Sometime later in Heaven's Arena, Chrollo finally meets Hisoka in combat, only for the both of them to start using the audience themselves as weapons for slaughter. When Chrollo kills him, Hisoka eventually rises from the dead and decided to cripple Chrollo’s power by starting to kill all members of the Phantom Troupe.

20 Makoto Shishio (Rurouni Kenshin)

Vengeful Rebel Who Wants To See Kyoto Burn

When it comes to people Kenshin Himura has crossed blades with in Rurouni Kenshin, none seem more fearsome compared to Makoto Shishio. A double-crossed former government assassin who survived being burned to death, Shishio established the Juppongatana with the intention of overthrowing the very government that betrayed him.

Compared to villains more motivated by a personal agenda, Makoto’s self-absorbed desire to destroy the government has transformed him into a cunning and ruthless person. He treats people as a means to an end and is even willing to cut through Yumi Komagata, perhaps the only one to ever love him, just so he can try to hit Kenshin. His ruthlessness is made even more terrifying by the fact that he’s once considered the Battosai’s successor, making his combat prowess on par with Kenshin’s. Minus the part at the end when Kenshin’s resilience finally prevails, Shishio has spent much of his arc pummeling the Battosai to the ground.

Claim To Infamy: The Attempt At Aoiya

When Shishio invites Kenshin to their duel to the death at Mount Hiei, the Juppongatana leader commits perhaps his most ruthless act: sending all but his most trusted allies to kill Kenshin’s friends at the Aoiya Inn. While Kaoru Kamiya, Misao Makimachi, and Yahiko Myojin held their own against the Juppongatana’s elite forces, the idea that Shishio sent his men to kill Kenshin’s lesser combat-capable friends is both cunning and cruel. This also demonstrates Shishio’s strategic prowess, correctly predicting that Kenshin will have his most powerful allies (Aoishi Shinomori, Sanosuke Sagara) accompanying him while his friends rest comfortably in the inn with no significant defenses.

19 Orochimaru (Naruto)

Did Everything For Power And Immortality

Despite being sidelined as a scientist figure in Boruto, Orochimaru is, in fact, one of the deadliest antagonists in the Naruto series. In the original Naruto anime, Orochimaru establishes his notoriety by not only studying Forbidden Jutsu but also stopping at nothing to achieve his goal of immortality. These included experimenting on unwitting subjects and even outright experimenting on himself to be capable of “transferring” himself to other bodies.

Such was his nature as a deadly character that he orchestrated the dreaded Konoha Crush that almost caused the destruction of the Hidden Leaf Village. He also served as Sasuke Uchiha’s mentor, training him to become a merciless shinobi. The only reason he hasn’t decided to become a villain in Boruto is his insistence on observing Sasuke’s “different” path, contrary to his expectations that the Uchiha survivor would choose to destroy Konoha.

Claim To Infamy: Human Experimentation

On top of his obsession with attaining immortality, Orochimaru’s unbridled curiosity also extends to unlocking the secrets of Forbidden Jutsu. Orochimaru at some point began kidnapping children and infants for his experiments with the First Hokage’s DNA. The goal of this horrific act was to see if any of them could replicate Hashirama’s unique Wood Release, with all children eventually dying during the experimentation process. When Hiruzen discovered Orochimaru’s horrific human experiments, the Sannin fled the Village. Only one child survived the experiment and developed Hashirama’s Wood Release: Yamato, an Anbu member who eventually became Naruto’s Team 7 Captain in Shipudden.

18 The Major (Hellsing)

Delighted In The Bloodshed Of War

In the alternate reality of Hellsing, it was Abraham Van Hellsing and his Royal Order of Protestant Knights that became the sole defense of the United Kingdom against the forces of the undead and the paranormal. Now led by Sir Integra Hellsing, a threat in the form of a Nazi group called the Millennium forced Integra to awaken the vampire Alucard, who was defeated by Abraham and forced into a life of servitude.

And despite the nonstop action Hellsing provides to fans, what perhaps serves as the series’ most perplexing figure comes in the form of The Major. Serving as the leader of the Millennium and the former first lieutenant of Adolf Hitler himself, the Major is hell-bent on ensuring that Fuhrer’s Order 666 was implemented, which in itself is a plan to artificially induce vampirism in the mass populace. What makes the Major especially gruesome is his ridiculous love for war, stopping at nothing to ensure violence is propagated throughout the series.

Claim To Infamy: The Zeppelin Affair

The Major’s obsession to wage war has been implied to border on the psychological-philosophical rather than mere capitalism, with the Millennium leader enjoying war seemingly for how sheer carnage manages to unravel the full extent of man’s free will and individuality. The full extent of this obsession is seen in what in-universe Hellsing newspapers would eventually call the Zeppelin Affair, a revived Millennium’s attack on London that would’ve escalated to a full-blown World War had it been left unchecked. This incident resulted in the slaughter of 3 million lives - which in itself should be tragic enough. However, the event could be further elevated to nightmarish horror when fans consider the added twist of the Major “conducting” his soldier’s carnage below atop his zeppelin throughout the course of events.

17 Father (Fullmetal Alchemist)

Didn't Mind Killing A Country If It Meant Having Power

In the region of Amestris in Fullmetal Alchemist exists the craft of Alchemy, a specialized science that involves transforming one object into the other. While protagonists Edward and Alphonse Elric have grown to become reliable State Alchemists throughout the course of Fullmetal Alchemist, it seems they have a much deeper relationship with their father, Van Hohenheim. This is especially true since Van Hohenheim has lived for hundreds of years, with his original name simply being “Number 23,” an alchemist in service to the King of Xerxes.

During this ancient time, Van Hohenheim managed to come into contact with the Gate - the origin of all knowledge - and “extract” a part of it. Known simply as the Dwarf in the Flask, it’s this being (called a homunculus) that taught Alchemy to the rest of the region. And after purging himself of sin, he’s adopted a colder, sadistic, and megalomaniacal persona as Father. In this form, his sole purpose was to transform the entirety of Amestris into a large enough transmutation circle to enable him to achieve the power of godhood, which Father had done for a limited time. In his most powerful form, he was even able to create miniature suns in the palm of his hand. It took the combined powers of Edward Elric and his other companions to finally defeat Father.

Claim To Infamy: The First Philosopher’s Stone

When “Father” was just a formless homunculus summoned by the King of Xerxes to teach alchemy, the creature was quick to befriend Prisoner 23, a fellow slave. And when the King revealed to “Father” his desire to learn the secrets of immortality, the homunculus lured the King into creating a city-wide transmutation circle to help him with his wishes. Afterward, Father orchestrated events to ensure they and the unknowing Hohenheim ended up at the center of the circle, using the city-wide bloodshed to conduct large-scale human transmutation. In his largest act of deception against the King, the homunculus sacrificed all souls within Xerxes to create the world’s first Philosopher Stone, channeling it to create a body in the visage of Hohenheim in order to control its powers.

16 Majin Buu (Dragon Ball Z)

A Being Created Only For Absolute Destruction

Initially appearing as the bubbly yet unpredictable pink monster in the latter part of Dragon Ball Z, the character of Majin Buu would end up becoming perhaps its strongest, most dangerous villain. While possessing many forms, the diminutive Kid Buu is his truest form, the one devoid of restraint and sanity. It’s also this form that Goku and his comrades had the hardest time defeating due to its absorption abilities, constant regeneration, and seemingly indestructible body.

However, what makes Majin Buu ruthless and terrifying is his personality — or lack thereof. Majin Buu lacks any remorse or compassion and seems incapable of comprehending empathy. Majin Buu enjoys destruction and finds amusement whenever he destroys worlds.

Claim To Infamy: Planetary Destruction To Search For Opponents

While Kaioshin already elaborated on the ferociousness of Kid Buu as an amalgamation of all evil, the lengths of his ruthlessness are seen firsthand during Buu’s battle with Vegeta and Goku on Earth. Not only did Kid Buu just casually destroy himself and all of Earth with the Planet Burst attack, but Kid Buu reformed himself from all the rubble and went on a rampage when he realized Goku and Vegeta were still alive. Before he locates them on Supreme Kai’s planet, it’s said that Kid Buu destroyed planet after planet in search of the duo. While this segment only happened in the anime for dramatic flair, it greatly demonstrated Kid Buu’s willingness to go no holds barred if it meant having a good fight before pursuing pure destruction.

15 Tamaki Tsunenaga (Deadman Wonderland)

Sadistic Warden Who Toyed With Prisoners

In the world of Deadman Wonderland, a devastating earthquake destroyed most of Tokyo and caused widespread destruction in Japan. While protagonist Ganta Igarashi seems like an ordinary 9th grader, a grisly massacre of his class had all evidence point to an innocent Ganta. Cornered and framed, Ganta had no choice but to go to the eponymous Deadman Wonderland as a death sentence, a prison-theme park run by the warden Tsunenaga Tamaki.

While Tamaki being the warden immediately puts him in the crosshairs of most Deadman Wonderland characters, it’s his relationship with them that makes him quite the menace. For starters, not only did he pose as Ganta’s lawyer, he actually rigged evidence against him. Moreover, beneath his goofy, idiotic, and always-smiling exterior is a sadistic nature that cares for nothing but finding ways to kill more prisoners for his amusement.

Claim To Infamy: Pitting Husband Against Pregnant Wife

Behind Tamaki’s ever-present smile is a sadist who relishes the idea of using prisoners of Deadman Wonderland as his playthings. One such act Tamaki enjoyed was the Carnival Corpse, a gladiator-style event that pits two prisoners in a fight to the death. After arranging a fight between Nagi Kengamine and his pregnant wife, Tamaki makes a deal with Nagi to not harm his wife if he throws his Carnival Corpse match. Instead, Tamaki goes back on his word and orders Nagi’s wife killed while he experimented with the unborn child.

14 Caster (Fate/Zero)

Morbid Amusement Is More Important Than A Wish-Granting Artifact

A character with immense power that has a penchant for inhuman acts shouldn’t be paired with a partner just as despicable, and yet this is exactly what happened to Gilles de Rais, assigned as the Caster Class of the Fourth Holy Grail War in Fate/Zero. In his rather tragic backstory, losing his love Joan of Arc drove him to insanity, resorting to alchemy and slaughtering children in a mockery of God’s absence during these horrible acts.

In Fate/Zero, Gilles de Rais is summoned as Caster after his Master, Ryuunosuke Uryuu, mistakenly uses a spellbook to create a summoning circle. Throughout the Holy Grail War, Caster and Ryuunosuke didn’t even spend time trying to fight their fellow Servant-Master pairs for the Holy Grail. Rather, Gilles de Rais served as an instrument to further Ryuunosuke’s curiosity about death, casually killing children and families for their amusement.

Claim To Infamy: Kidnapping, Torturing Children

Fate/Zero provides the opposite end of the “Master unaware of the Holy Grail War,” as naive but heroic Shiro Emiya of Fate/Stay Night meets his match in the serial killer Uryu Ryuosuke. It’s not enough that Uryu “accidentally” summoned Caster using the blood of a family he murdered, but the Holy Grail pairing Uryu with Gilles de Rais’s sadistic nature led to one of the biggest threats in the Fourth Holy Grail War. While absent for most of the fighting, this time was also when they had done the most horrific act in the show: kidnapping children and using them for experiments. While Uryu commits horrific acts of torture on these victims, Gilles impresses Uryu by using them for black magic. Such was their threat that all war hostilities were halted and a kill order was issued on Uryu and Caster.

13 Frieza (Dragon Ball Z)

Likes Toying With His Opponents

Majin Buu might have been the strongest villain of Dragon Ball, but none could match Frieza in terms of sheer evil. His charm and mercilessness maintain his popularity among fans, to the point of being the most recurring villain in the Dragon Ball franchise. During his time as ruler of the galaxy, Frieza exterminated of the entire Saiyan race. Prior to his demise at the hands of Goku, Frieza freely toyed with his friends and comrades.

Boasting the power of transformation, Frieza always keeps his enemies on their toes and takes delight in taunting and torturing them for his amusement. His intelligence makes his sociopathic nature all the more horrifying. Some of his infamous acts include causing Krillin to explode and destroying Namekian villages in his pursuit of the Dragon Balls.

Claim To Infamy: Killing Krillin

While Frieza has demonstrated the capability of destroying entire planets on a whim, it’s when he truly makes an effort to kill someone that demonstrates the depths of his ruthlessness. This is especially seen with Krillin who, despite being one of Earth’s best martial artists, could barely hold a candle to Frieza’s ever-growing power level. When Frieza unleashes his second form, he mercilessly gores Krillin on the abdomen with his horns. Moreover, when he realizes Krillin’s importance to Goku, he telekinetically raises him into the air and makes him self-destruct for dramatic effect and to see Goku suffer.

12 Kyubey (Puella Magi Madoka Magica)

If Saving The World Needed The Sacrifice Of Kids, Then So Be It

Despite its appearance, Kyubey of Puella Magi Madoka Magica is more than just a cute cat-like mascot. Kyubey is an Incubator, a member of an advanced civilization hell-bent on stopping entropy from killing the universe. Kyubey and his species discover that emotions, particularly from teenage girls, can help prevent the spread of entropy. Kyubey approaches these girls and offers to grant their wishes in exchange for fighting witches, not telling them that they will become witches themselves after being exhausted from their emotional energy.

Kyubey’s abject lack of empathy makes its actions more terrifying. For their species, it’s worth sacrificing the lives of these magical girls if it means stopping the eventual death of the universe. And Kyubey won’t hesitate to discard a magical girl whom it finds useless. It’s possible that once the human race is devoid of magical girls, Kyubey will simply find another species capable of producing such emotions and repeat the cycle.

Claim To Infamy: The QB Agenda

Madoka’s Magical Girl companions slowly dying at the hands of Witches prompts Kyubey (QB) to explain the whole point of their endeavors: using the potent magic of grieving young girls to fight the rise of entropy and stop the heat death of the universe. While QB’s species lack the emotion to manifest this magic, their science is advanced enough to create methods of tapping into them. It’s soon revealed that Kyubey has created the very cycle they were in to produce entropy-fighting magic: create Magical Girls who kill Witches for their energy, turn Magical Girls into Witches using their suffering, and create more Magical Girls to fight them. As girls Madoka’s age just so happens to be filled with hope, they can easily be roped into their “duties” as the universe’s protectors. Unfortunately for Madoka, Kyubey likely only sees this convenience in an objective way, as he has no emotional capacity to see any of his actions as “wrong.”

11 Makishima Shogo (Psycho-Pass)

Feel Genuinely No Remorse For Murders

In the future Japan of Psycho-Pass, the enigmatic Sybil System can instantaneously quantify and measure a person’s mental state, using said information to determine someone’s “perfect” place in society. However, the Sybil System requires people to have a low "Psycho-Pass," a propensity for violence. The police hunt down individuals with a high Psycho-Pass.

Makishima Shogo, the first season’s central antagonist, conducts mass murder with a low Psycho-Pass. Despite his murderous intent, his Psycho-Pass remains low because he thinks of his crimes as sound and reasonable. One might think he kills solely to mock the system that thinks it's perfect, which makes Makishima all the more horrific.

Claim To Infamy: The Killing Of Yuki Funahara

One of the most startling displays of Makishima Shogo’s ruthlessness is his merciless killing of Yuki Funahara, Akane’s best friend who isn’t remotely involved in her police work. In this confrontation, Makishima takes a shaving blade and nonchalantly slits Yuki’s throat. However, what made this ordeal all the more horrific for Akane is the fact that her Dominator gun specifically designed to trigger at signs of criminal intent never activated at the sight of Makishima’s act of murder. In their world where a person’s emotions and criminal intent are “quantifiable” by the Sibyl System, if an all-encompassing AI doesn’t register Makishima’s murders are done with ill intent, then the Sibyl System’s “perfect” society may fall apart.

10 All For One (My Hero Academia)

Wants To Plunge Humanity Into An Age Of Darkness

While the first few appearances of the League of Villains revealed them as rather run-off-the-mill “villains of the week” that the Pro Heroes always seemed to defeat, they eventually began abusing the popularity of their professional rivals by systematically ruining their public image while leaving them ripe for attacks and abuse. Such a tactic could only be conceived by someone aware of how human malice works, and legendary hero All Might of My Hero Academia is correct in deducing this was the work of All For One.

As the bearer of the powerful All For One Quirk, the villain is capable of stealing and bestowing Quirks upon others. He even transformed his younger brother into the first bearer of the inheritable One For All Quirk - out of pity, as he’s born Quirkless. All For One would be infamous before the series’ timeline as a leader of villains who recklessly use their powers. And in the current age of Pro Heroes in My Hero Academia, All For One would train an apprentice to carry on the legacy of the League of Villains, and eventually ruin his psyche enough to become his Quirk and persona’s new host.

Claim To Infamy: Wanted To Become An All-Powerful Evil God To Rule Humanity

All For One’s cruel nature extends to his tactical acumen, as his plan to create a host for his unstable Quirk took decades to come to fruition. Near the end stage of his plan, he successfully eliminated his rival All Might from the board by forcing him to use the last of his One For All essence, as he knew his kid apprentice (Izuku Midoriya) can barely control its powers. Moreover, All For One built this momentum exactly to allow his apprentice, Tomura Shigaraki, to begin a more aggressive approach to the League of Villains in their bid to conquer the world. To add insult to injury, he chose Tomura specifically to insult the memory of Nana Shimura - Tomura’s grandmother, All Might’s teacher, and All Might’s predecessor as the One For All’s wielder.

9 Naraku (InuYasha)

Evil For The Sake Of It, And For Fun

Compared to other creatures encountered in Inuyasha’s journey for the crystal shards, Naraku is perhaps the most detestable among them. A hanyo or half-demon like Inuyasha, Naraku of InuYasha has completely absorbed his potential to do evil. Such was Naraku’s inherent power that he not only possesses the abilities of transformation and nigh-immortality by body recomposition, but he can also absorb the powers of other demons. These abilities are also combined with his keen cunning and intellect, which are traits he always uses to outsmart his opponents.

Such is Naraku’s infamy in InuYasha that the creature is held responsible for causing all the misfortune in the lives of most, if not all, the main cast of characters. What’s worse is that Naraku’s infliction of these trauma and catastrophic events is almost always for his amusement. While it’s eventually revealed that he’s simply an agent for a darker power, Naraku’s unnecessary vigor in adding salt to wounds makes him a horrifying villain to encounter.

Claim To Infamy: Tormenting Sango

While Naraku had caused harm among all members of Inuyasha’s troupe even before they met, his tormenting of Sango may have been his most ruthless act. Shortly after the shattering of the Sacred Jewel, Naraku manipulated the head of Sango’s demon slayer village as well as her brother Kohaku into slaughtering demon slayers, causing Kohaku’s eventual death. When Naraku discovered Sango survived, he manipulated her into killing Inuyasha. Upon failing this act, Naraku resurrected Kohaku in an attempt to play with Sango’s emotions across the series. While it’s revealed that this was all Naraku’s plan to corrupt the Sacred Jewel Shard, Naraku going to such an extent to torment Sango was excessive.

8 Bondrewd (Made In Abyss)

Children Were A Part Of His Experiments

The small town of Orth gained notoriety for surrounding a giant hole known only as the Abyss, the eponymous setting of Made In Abyss. It’s said that the Abyss contains remnants of ancient civilizations and artifacts of dangerous qualities, attracting various adventurers known only as Cave Raiders. When protagonist Riko discovers that her mother, White Whistle Lyza, may be alive deep within the Abyss, she takes the robotic Reg with her and ventures forth. Throughout their journey, they eventually discover the existence of Bondrewd, the Lord of Dawn, one of the most legendary White Whistle Delvers to ever exist.

Unbeknownst to Riko, Bondrewd harbors a rather dark secret. Fascinated by the nature of the Abyss, Bondrewd has made it his life’s mission to conduct research on the Abyss’s netizens, employing various methods to get the data he needs. Inside his base called the Ido Front, Bondrewd conducts sadistic experiments with no signs of remorse.

Claim To Infamy: Cartridges

Bondrewd seemingly had to discard the idea of morality to continue his endeavor in researching the wonders of the Abyss, to the point of using humans for his experiments for the “good of all.” Perhaps his cruelest act would be creating Cartridges or special packages that help Bondrewd fight the Curse of the Abyss especially since he stays in its deepest reaches. What makes Cartridges so horrifying is how it’s composed of humans who “won’t be missed” and are the “easiest to transport,” soon implying that Cartridges are composed of the brains, spines, and enough organs of kidnapped children. Drugs are kept in the briefcase to retain both terror and ecstasy in victims as the brunt of the Curse is put onto them and not Bondrewd.

7 Yami Marik (Yu-Gi-Oh!)

A Manifestation Of Evil In A Children's Show

When Seto Kaiba announces the Battle City Tournament, he does so with another agenda aside from having another shot at defeating Yugi Muto. Rather, he does so at the request of the clairvoyant Ishizu Ishtar, who wishes to lure his brother Marik out of hiding in the hopes of regaining control of the God Cards and ensuring he can’t use them to wreak havoc in the world. Throughout the series, Marik disguises himself as “Malik” to befriend Yugi and his peers, all the while using the Millennium Rod to control his minions to engage them in lethal Shadow Games.

As it turns out, the Ishtar bloodline was sworn guardians of the Pharaoh’s tomb, and their lives forbade them from ever interacting with the outside world. This traumatized a young Marik, who was physically and emotionally abused by his father. With the presence of the Millennium Rod eventually manifesting his evil side into an actual persona, the weaker Marik was shelved aside by this malevolent figure who wishes nothing but to see the Pharaoh in Yugi Muto suffer and eventually die.

Claim To Infamy: Shadow Games Consisted Of Lethal Traps In A Children's Show

Among the villains in the Yu-Gi-Oh! series, Yami Marik has perhaps the most sadistic streak. Born out of the malice in Marik Ishtar’s heart, Yami Marik stands as one of the unique villains in the original series who wasn’t a “spirit” from Ancient Egypt sealed into an item, but rather pure malevolence given form. As such, it’s surprising for a kid-oriented show to have Yami Marik utterly killing Marik’s abusive father during his first possession and even going to such lengths as attempting to maim or kill Yugi and his friends in the Battle City Arc. These are evidenced by Yugi’s fight with Arcana that involved foot-cutting saws, or a literal death match between Yugi and a possessed Joey Wheeler that would force the protagonist between saving himself or his friend. In the semis, Yami Marik would render both Joey and Mai Valentine in catatonic states. Even his final battle would be a sight for such horrors, with Yami Marik forcing Yami Yugi to wager the souls of both his original form and Yugi Muto in the finals.

6 Shou Tucker (Fullmetal Alchemist)

Who Believed Experiments Can Include Family

Despite only appearing for a few episodes, Shou Tucker of Fullmetal Alchemist made a horrifying mark on its viewers, showing what can result from unbridled ambition and irresistible curiosity. The foremost expert in chimeras, Shou Tucker lives with his daughter, Nina, after his wife left them. Shou earned his State Alchemist License on the promise of producing a chimera capable of speech.

Unfortunately, he doesn't produce any results until he comes up with a horrifying solution: fusing Nina and their family dog, Alexander. When confronted, Shou tries to justify his depravity with the explanation that all scientific advancements are founded on a price. It’s this mercilessness of sacrificing his daughter in the name of science that makes Shou so deplorable in the eyes of fans.

Claim To Infamy: Nina Tucker

Shou Tucker’s most horrific act is precisely what sent him as well as his daughter Nina and their dog Alexander into meme pages. Desperate for results in his research on creating chimeras, he makes one out of his remaining family. As a result, Shou merges Nina and Alexander into one being, creating a chimera that Scar has to mercy kill in order to put them out of their misery. Despite Shou’s short stay in the series, this one act cemented that Fullmetal Alchemist won’t shy away from showing the horrific implications of alchemy and human desperation, as well as measures others will take in attempts to save those involved.