Seiji Shishikura, a second-year student at Shiketsu High School training to become a Pro Hero, comes from a family associated with hero society. His father served at Tartarus prison and was responsible for escorting All For One to his cell; the prison guards' commissar-style hats influenced Seiji's choice of Shiketsu High due to its similar uniform aesthetics. Physically, Seiji possesses purple hair styled with a fringe covering his left eye and thin, slanted black eyes. He exhibits insecurity about his eyes, especially when mocked by Katsuki Bakugo. His hero costume includes a black overcoat with red trimmings, a high neck collar, armbands, Shiketsu's signature hat, and fingerless gloves covering only his thumb, index, and middle fingers. Post-graduation, he retains a refined version of this costume while serving as a prison guard captain. Seiji embodies a stern, dignified persona, heavily valuing Shiketsu's principles of obligation and tradition. He believes heroes must act with decorum and openly condemns those he deems undignified, particularly U.A. High's Class 1-A students like Bakugo, whose vulgarity he views as tarnishing heroism's image. During the Provisional Hero License Exam, this mindset leads him to prioritize eliminating "unworthy" candidates over passing himself. He compresses multiple examinees—including Eijiro Kirishima and Bakugo—into immobilized flesh balls retaining sentience using his Quirk, Meatball. His condescension causes him to underestimate opponents like Denki Kaminari, who defeats him with a coordinated counterattack involving Bakugo and Kirishima, resulting in Seiji failing the exam. His Quirk, Meatball, allows him to manipulate raw flesh. Against others, he compresses them into immobilized flesh balls retaining sentience. With his own flesh, he detaches and reshapes it for offense (e.g., projectiles) or defense (e.g., shields), controlling it remotely. Stat-wise, he excels in technique and vocabulary but has average physical power and speed. Seiji's rigidity stems from influence by the Hero Killer Stain's ideology, though he denies this association. Teachers note his inability to self-reflect or acknowledge flaws, as he imposes his standards onto others. Despite this, he shows concern for classmates; he berates Camie Utsushimi's free-spirited nature but feels guilt for not recognizing her impersonation by Himiko Toga during the licensing exam. Relationships define key aspects of his behavior. He respects Inasa Yoarashi for his passion and dignity, accepting Inasa's deference as "senpai." Conversely, his animosity toward Bakugo is mutual, marked by verbal sparring over Bakugo's crudeness and Seiji's eyes. His elitism isolates him from peers except Inasa, who overlooks his harshness. During the Final War, Seiji confronts All For One, who murdered his father. Though he admits wanting vengeance, he suppresses his rage to avoid succumbing to villainous tactics, instead honoring his father's legacy by focusing on protecting others. Eight years post-war, he becomes the No. 41 Pro Hero and serves as Tartarus' guard captain.