Eijiro Kirishima trains as a Pro Hero student in U.A. High School's Class 1-A. His Quirk, Hardening, grants rock-like skin, enhancing durability and strength to withstand physical attacks, blades, bullets, and explosions. Effectiveness and duration rely on his willpower; prolonged use or severe damage weakens or cracks it. His ultimate move, Red Riot Unbreakable, pushes his Quirk to its limits for about 40 seconds, drastically increasing durability and offense while sacrificing mobility. A specific weakness remains at his chin, leading him to wear protective gear there. Accidentally activating Hardening at age three, Kirishima hardened his hand and cut his right eye, leaving a permanent scar and initial dislike for his power. He later idolized the hero Crimson Riot, embracing the philosophy that a "manly spirit" of courage and self-improvement outweighed Quirk strength. Middle school found Kirishima introverted, insecure, with natural black hair. He failed to act when bullies threatened an underclassman and froze in fear when a menacing figure endangered classmates, actions Mina Ashido courageously resolved. Humiliated by his inaction, he nearly abandoned his U.A. dream until rediscovering a Crimson Riot interview. Inspired by the hero admitting fear but stressing action to avoid regret, Kirishima recommitted to heroism. He apologized to those he failed, intensified training and studies, and adopted his spiky red hairstyle as a symbol of resolve. At U.A., Kirishima presents as boisterous, outgoing, and chivalrous, frequently calling admirable actions "manly." He values bravery, honesty, and self-sacrifice, condemning cowardice and deceit. His determination to live without regret fuels his relentless protection of others, even at personal risk. Despite his confident exterior, he harbors self-doubt about his Quirk's perceived lack of flashiness compared to peers like Katsuki Bakugo or Shoto Todoroki. Academically moderate in Class 1-A, he often studies with Bakugo with limited success. His combat prowess is notable: second place in the U.A. Entrance Exam, eighth in the Quirk Apprehension Test. Key battles include fighting alongside Bakugo at U.S.J., drawing with Tetsutetsu Tetsutetsu in the Sports Festival due to identical Quirks and styles, and forcing Bakugo on the defensive before losing their match. Character development intensifies during the Internship Arc under Fat Gum. Facing Kendo Rappa, Kirishima falters after one punch, overwhelmed by memories of past cowardice. Rallying, he activates Red Riot Unbreakable to shield Fat Gum from Rappa's barrage, enduring the assault and enabling Fat Gum's counterattack. This act earns respect from allies and enemies, with Rappa requesting a rematch. His loyalty drives him to break school rules, organizing the mission to rescue Bakugo during the Hideout Raid Arc, blaming himself for the capture. Throughout later arcs, including the Shie Hassaikai Raid and Final War, Kirishima consistently prioritizes protecting others, scaling Gigantomachia to deliver sedatives and shielding Hitoshi Shinso from All For One. Eight years post-war, he graduates U.A., serves as Fat Gum's sidekick, achieves the rank of No. 12 Pro Hero, and retains his signature appearance and costume.