Eijirō Kirishima wields the Quirk Hardening, enabling him to solidify any part of his body, drastically boosting his durability and physical strength. This power shields him from physical dangers like explosions, bullets, and falling debris. However, hardening restricts movement in affected areas, weakens under continuous heavy force, and lasts roughly ten minutes before he needs to breathe. His ultimate move, Red Riot Unbreakable, grants near invulnerability for 30–40 seconds but leaves him severely exhausted. Training enhanced his Quirk's density and resilience, allowing it to adapt to damage. He gained a small scar above his right eye at age three when his Quirk activated unexpectedly as he rubbed his eye, causing his hardened hand to scratch it. This incident initially made him dislike his ability, despite his admiration for the hero Crimson Riot, who possessed a similar Quirk. In middle school, Kirishima struggled with cowardice, failing to intervene when others were in danger. Witnessing Mina Ashido defend underclassmen deepened his insecurity, especially as peers noted her heroic potential while he felt powerless. Inspired by Crimson Riot's speeches on courage and chivalry, he resolved to change, dyeing his naturally black hair red and styling it into spiked "horns" as a symbol of his new, fearless identity. Kirishima entered U.A. High School to become a Pro Hero, placing second in the entrance exam through balanced combat and rescue efforts. Academically, he started poorly but improved through diligent study, aided by Katsuki Bakugo. His Quirk placed him eighth in the initial Apprehension Test. Kirishima is boisterous and champions "manliness," using the term to describe bravery, determination, or noble conduct. He openly criticizes cowardice or dishonor and is moved to tears by displays of resolve. He readily befriends those exhibiting such traits, including Bakugo and Izuku Midoriya. Possessing a strong sense of responsibility and loyalty, he will break rules to protect others, as seen when advocating for Bakugo's rescue after a villain abduction. He engages in self-criticism after failures but uses this to drive his growth. Physically, Kirishima is muscular with light skin, red eyes, and pointed teeth. He maintains his signature red, spiked hair with gel and stands 170 cm (5'7") during his U.A. years. His hero costume features gear-shaped shoulder pads, a belt with an "R" insignia, a ripped half-cape, face gear resembling fangs, and later added arm sleeves to protect civilians during rescues, creating an oni-like appearance. He developed mutual respect with Bakugo during the U.S.J. incident and Sports Festival, where they fought evenly before Kirishima's Quirk weakened. Their dynamic evolved into one of equals. Interning with Fat Gum, Kirishima played a key role in raids, notably protecting Tamaki Amajiki and confronting the villain Rappa. Though initially overwhelmed, he regained resolve by recalling his past insecurities, activating Unbreakable to withstand Rappa's attacks, earning admiration from Fat Gum and Rappa. Later, Kirishima participated in rescuing Eri and fought in the Paranormal Liberation War. He helped subdue Gigantomachia by delivering a sedative and mourned Midnight's death. He joined efforts to retrieve Midoriya during the "Dark Hero Arc," preventing injuries during a confrontation. By the story's conclusion, he graduated and became the Pro Hero Red Riot, ranked No. 12.