The world of My Hero Academia is filled with heroes and villains who battle for supremacy. While the villains try to destroy the order that's been established, the Heroes do their utmost best to prevent that from happening. Over time, the conflict between the two has only grown and even wars have broken out recently, leading to countless deaths.
While some of the deaths in the series have certainly been deserved, there are quite a few that simply served either no purpose or were written not all that well.
5 Star And Stripe
Cathleen Bate, also known as Star And Stripe, was the number one Hero in the United States of America in the world of My Hero Academia. Her Quirk, known as New Order, was known to be one of the most incredible powers that could redefine what a quirk really is.
Cathleen was one of the very few female characters who are actually powerful in the series. Yet, just a few chapters after her introduction, she was killed off. Cathleen served as simply a stepping stone for Shigaraki and All For One. She was certainly not a character that was allowed to stand on her own and the writing, despite having quite a lot of potential, was quite subpar. Without a doubt, Star and Stripe should have had a major role to play in the series, especially since she was the number one Hero, and her death was untimely.
4 Magne
Magne was a member of the League of Villains at one point and she met her death during the Shie Hassaikai arc. When the league met with Chisaki for the first time, the meeting was quite tense and ended with Magne's death. By using his power to deconstruct people, Chisaki was able to kill her with a single touch of his palm.
While it was certainly possible for him to kill Magne, the character ended up being used as nothing more than a demonstration of Chisaki's deconstruction powers and lost all value in the process. To show off his abilities, Horikoshi could certainly have devised better ways which let the character demonstrate his might and not sacrifice others' value at the same time.
3 Sir Nighteye
Sir Nighteye was one of the most influential characters in My Hero Academia's Shie Hassaikai arc. Being the leader of the Nighteye Agency, he mentored Deku and Mirio at the same time. Nighteye was certainly a very skilled Hero and his power to see the future was quite incredible.
Without a doubt, he would certainly have been useful in the future of the story, however, towards the end of the arc, he was eventually killed off. While there is no denying that he was not the strongest of characters and, thus, always had death looming over his head, the way he died should certainly not have been enough to kill a Pro Hero as skilled as him. Mirio, his student, took similar injuries and managed to live. Nighteye, had Horikoshi intended it, could have survived quite easily. With all the recovery methods seen in the series, his survival should have been possible.
2 Twice
Twice was one of the most important characters in the Paranormal Liberation Front, being one of their Lieutenants. From the Villains' side, he was certainly a prominent figure from the very beginning of the story and had only grown on the fans even more in the recent arcs. Twice was also quite friendlier when compared to the other villains and his friendship with Hawks was proof of that.
During the Paranormal Liberation War arc, however, he met his death at Hawks' hands. For someone with a kind heart such as Twice, dying in betrayal certainly felt off. Furthermore, Twice's Quirk, double, was said to have the power to take down a nation if he so intended. Despite that, Hawks was able to dispose of him quite easily without even facing much of a challenge. Without a doubt, Twice died way too easily and for that reason, he also makes the list.
1 Many One For All Users
The majority of the users of the One For All Quirk are all dead. Currently, the Quirk is wielded by Izuku Midoriya, the protagonist of the My Hero Academia series. Prior to him, All Might, the Symbol of Peace, possessed this power. Aside from those two, every other user of the One For All Quirk has died. While that certainly isn't all that surprising, the manner of their deaths is rather redundant. Every user of the One For All, aside from the third, who died of old age, has been killed by All For One.
That's not to say that All For One doesn't possess the power to kill anyone he wants. It simply means that, on Horikoshi's part, having every user of the power die in a similar manner without any further explanations is a tad lazy. Fans don't know much about these deaths and how they came about, just that All For One eventually managed to dispose of them all, despite them being significant characters.