The characters of each title in the Persona series are arguably some of the strongest aspects of each game. It's typically pretty easy to identify and become invested in at least one party member of each game that ends up being a staple to who you choose to bring with you into each dungeon.
Unfortunately, in the rosters filled with such strong personalities, some characters are often overshadowed by others that are championed in the fandom. In some cases, the underrated characters are actually the most interesting ones in their respective titles that deserve to be talked about more.
10 Chie Satonaka
Chie is one of the original party members that join the investigation team of Persona 4. Her upbeat personality has proven to be very divisive among fans—some would go to bat with her, while others can't seem to stand her.
Chie has always been a bit underrated due to the fact that Yukiko is so frequently pushed by the game's narrative to seem more preferable as a romanceable candidate to the player. However, at the end of the day, she's one of the most forthcoming characters towards the player throughout the entire game, is one of the most powerful party members, and has compelling character growth throughout the series.
9 Junpei Iori
Junpei is the resident "bro" of Persona 3. He can be a bit hardheaded and act irrationally at times, but his arc involving Chidori proves that he has a heart of gold with good-intentions. Unfortunately, players of the original Persona 3, and not Persona 3 Portable, didn't really get to know Junpei that well, since he originally did not have a social link available. Players that got to experience Junpei's social link in Persona 3 Portable were treated to Junpei's more serious side, and not simply the comic-relief that he's mostly known for.
8 Ann Takamaki
Ann is similar to Chie in the sense that she has the unfortunate role of being overshadowed by the other female party members in Persona 5. Ann has most of her characterization in the beginning of the game, showing her dedication to her friends and her strong resolve for justice, but unfortunately, her narrative is put on the backburner in a sense for the rest of the game (characters like Makoto and Futaba really start to be emphasized more).
This is unfortunate because Ann is a character with one of the more stronger personalities in the game. She has an interesting history and background that doesn't seem to be discussed very often.
7 Koromaru
Koromaru obviously receives a decent share of attention, since he's a dog with a persona. But that's mostly the extent of how he's typecast throughout the game: the mascot animal companion.
By exploring the dialogue and files of Persona 3, players can learn more about Koromaru's life, his loyalty to his previous owner and the lore that he is based on (Hachikou, a famous figure in Japanese history).
6 Kanji Tatsumi
The dungeon and circumstances that Kanji is recruited in typically encompass how players remember him: his conflicting feelings towards masculinity and sexuality. While that is definitely the most compelling aspect of his personality, it really pushes aside the growth that Kanji experiences throughout the game, and how his relationship with the main character is pivotal for his development.
Kanji confides in the player that the main character is like a mentor-figure to him, and admits that he's a huge reason for accepting who he is and not feeling ashamed for his interests any longer. It's a heartwarming example of some of the best character development in the game, but it's often lost on the fact that people only associate him with his sexuality.
5 Haru Okumura
The last party member to be recruited in Persona 5, Haru has often been discussed as being a great character that fell victim to being introduced too late. Unlike the other characters who have time to show character development organically throughout the events of the game, Haru joins the Phantom Thieves when they're already very established. Her confidant needs to be completely rather quickly as time is scarce once it becomes available, so many people end up not completing it.
This is unfortunate because Haru is actually a very complex character with an interesting background. She may seem soft and timid, but she actually has a feisty and even somewhat sadistic side to her.
4 Yukari Takeba
One of the most divisive characters in the series, Yukari's personality can be summed up as either: you love her, or you hate her. To be fair, Yukari had a difficult upbringing, through losing her father and her mother's inability to cope with his death. She can come off a bit abrasive, but if the player chooses to pursue her social link, she opens up to the main character, and her acerbic tone starts to make more sense.
3 Yusuke Kitagawa
Yusuke is definitely the most eccentric party member in Persona 5 (save Morgana since, y'know, he's a talking cat). He's stoic with a goofy side, a bit feminine, and loves art.
He's not for everyone, but he's also unlike most party members that we've seen throughout the series, and his more out-there personality is refreshing in comparison to some of the redundant characters we meet in each game (see: Junpei in Persona 3, Yusuke in Persona 4, and Ryuji in Persona 5 who essentially all share the same personality).
2 Metis
Metis only appeared in The Answer of Persona 3: FES as the dark side of Aigis' personality. She doesn't have the best introduction in terms of likability, as she almost kills Ken, but she's arguably the most interesting character throughout The Answer, especially given her relationship to Aigis. Unfortunately, as the two merge back together in the end, Metis doesn't appear again, and isn't really talked about much.
1 Female Main Character (Persona 3 Portable)
Similar to Metis, the female protagonist of Persona 3 Portable is a character that not many Persona fans know about (or know much about). She breaks the traditional mold of protagonists in the series being a bit bland, and is actually characterized significantly in the dialogue choices that are presented to players when she is selected to be played as in the story. Luckily, her fanbase was vocal enough to convince the developers to have her return in Persona Q 2.