Eijiro Kirishima trains as a student at U.A. High School to become a Pro Hero, ultimately achieving the rank of No. 12 Hero eight years after the Final War. His journey began with significant transformation. As a junior high student at Mustafa Private Middle School, Kirishima grappled with self-doubt and fear, feelings intensified after witnessing Mina Ashido successfully intervene against bullies and confront a threatening figure. His own hesitation during an incident nearly shattered his dream of attending U.A. High. However, discovering an interview with his idol, Crimson Riot—who championed living without regrets despite fear—reignited his resolve. Kirishima trained rigorously, passed the U.A. Entrance Exam with the second-highest score, and reinvented his appearance by dyeing his naturally black hair bright red and styling it into spiky "horns" as a symbol of his commitment. His Quirk, Hardening, enables him to harden and sharpen any part of his body, granting enhanced durability and strength. It first manifested at age three, accidentally scarring him above his right eye. The Quirk's durability scales with Kirishima's willpower and exposure to damage, as each hardened layer grows stronger after impact. Limitations include reduced mobility at maximum hardness and vulnerability to prolonged, high-intensity attacks. Kirishima developed techniques like Red Riot Unbreakable, his ultimate move, which pushes his Quirk to its peak for approximately 40 seconds, providing near-impenetrable defense at the cost of extreme stamina drain. Kirishima's personality is marked by boisterous enthusiasm, a focus on "manliness" (equating it with bravery, selflessness, and chivalry), and fierce loyalty. He forms strong bonds, particularly with Katsuki Bakugo, whom he admires for strength and determination. Their friendship began fighting villains side by side during the U.S.J. incident and deepened when Kirishima spearheaded Bakugo's rescue from the League of Villains. Kirishima's empathy and lack of condescension made him one of the few Bakugo respects. His relationship with Mina Ashido originates from middle school, where her actions initially deepened his insecurities. At U.A., they became close friends, with Mina encouraging his growth. Kirishima later protected her during the Paranormal Liberation War, acknowledging she had always been his hero. Key developments include Kirishima interning under Pro Hero Fat Gum, debuting Unbreakable to shield civilians from a blade-wielding villain enhanced by Quirk-boosting drugs. During the Shie Hassaikai raid, he withstood Kendo Rappa's barrage of punches to protect Fat Gum, earning recognition from both. His perseverance embodied his mantra of being "a horse that never wavers," a mindset reinforced by Bakugo's encouragement. In the Final War, Kirishima and Fat Gum jointly blocked a catastrophic attack from Tomura Shigaraki, aiding the heroes' victory. Post-graduation, Kirishima works as a Pro Hero, retaining his signature spiky hair and hero costume with minor updates. His journey reflects continuous growth from a regretful adolescent into a resilient protector, guided by Crimson Riot's ideology and his unwavering commitment to living without regrets.