Katsuki Bakugo grew up alongside Izuku Midoriya, known early for his confidence, energy, and natural talent in activities like reading and physical coordination. His powerful "Explosion" Quirk manifested later, enabling him to detonate nitroglycerin-like sweat from his palms. Constant praise for this ability fueled a superiority complex and aggressive tendencies, particularly directed at the Quirkless Izuku, whom he bullied relentlessly with the derisive nickname "Deku." This behavior intensified after an incident where Izuku offered help when Katsuki fell into a stream; Katsuki perceived this as condescension, deepening his resentment. Enrolling at U.A. High School's Hero Course alongside Izuku challenged Katsuki's perspective. He initially dismissed classmates as "extras" and struggled with Izuku's sudden Quirk manifestation, seeing it as deception. Early academic achievements highlighted his strategic intelligence and combat prowess, yet defeats—notably by Izuku during training—began to erode his arrogance. His fixation on victory remained absolute, demanding opponents like Shoto Todoroki use their full power during the U.A. Sports Festival tournament. He won the tournament but rejected the gold medal, deeming Shoto's restraint an invalid victory. Kidnapping by the League of Villains became a pivotal trauma. Rescued by All Might, Katsuki blamed himself for All Might's subsequent retirement after the battle depleted his powers. This guilt manifested in withdrawn behavior and failure in the Provisional Hero Licensing Exam. He later confronted Izuku, deduced the secret of One For All, and fought him to process his emotions. All Might intervened, absolving Katsuki of blame and revealing the truth about One For All and All For One. This confrontation marked a turning point; Katsuki began training with Izuku to help him master One For All's emerging Quirks, signaling a shift toward cooperation. Further development occurred during internships and missions. His internship with Best Jeanist temporarily modified his appearance and costume to seem less intimidating, though he retained his core personality. During the Paranormal Liberation War, Katsuki instinctively took a fatal blow meant for Izuku, an act of selflessness highlighting his growth. Edgeshot resuscitated him, leaving a prominent suture scar on his chest. Later, during Izuku's self-imposed exile, Katsuki delivered an apology, admitting his past bullying stemmed from insecurity over Izuku's innate heroism and jealousy of his bond with All Might. This vulnerability solidified their renewed rivalry and friendship. In the final war against All For One and Tomura Shigaraki, Katsuki sustained severe injuries, including a crushed right arm and heavy scarring on his right cheek. He utilized All Might's armored support gear as a splint. After contributing to All For One's defeat and enabling Izuku's final strike against Tomura, he underwent extensive rehabilitation, eventually regaining full use of his arm. Post-graduation, he worked as a sidekick under Best Jeanist before ascending to the rank of Pro Hero, reaching No. 5 nationally. His costume retained its core design but featured streamlined grenade bracers resembling smoke grenades. By adulthood, he adopted a more muscular physique and wore braids resembling lit fuses, embodying his hero name: "Great Explosion Murder God Dynamight." Throughout his journey, Katsuki's core drive—to surpass All Might and become the No. 1 Hero—remained unwavering. However, his methods evolved from solitary aggression to strategic teamwork, his respect for peers like Eijiro Kirishima and Shoto Todoroki grew, and his relationship with Izuku transformed from animosity to a fiercely supportive rivalry. His abrasive demeanor, blunt honesty, and explosive temper persisted, integrating with a deepening sense of responsibility, self-awareness, and commitment to saving others.