Toshinori Yagi, publicly celebrated as All Might, entered a chaotic world dominated by the villain All For One as a Quirkless child. Family loss to violence ignited his resolve to become a hope-inspiring hero. As a teenager, he recklessly charged villains with a lead pipe only to be intercepted by Nana Shimura, seventh holder of One For All. Captivated by his vision for a "Symbol of Peace," she mentored him and transferred One For All before his U.A. High School enrollment. At U.A., Nana and her associate Gran Torino subjected him to grueling training; Gran Torino’s severe methods accidentally embedded a lasting fear within him. In his final U.A. year, Toshinori, Nana, and Gran Torino clashed with All For One in a ruinous confrontation. Nana died ensuring Toshinori’s escape, compelling Gran Torino to shield him. Consumed by grief and vengeance, Toshinori accepted Gran Torino’s counsel to train in America, evading All For One’s reach. Post-graduation, he embraced his iconic smile and left for the United States. There, Toshinori launched his hero career by saving scientists including David Shield, who became his confidant and designed his initial costume. He rescued young Cathleen Bate, inspiring her rise as America’s top hero Star and Stripe, and encouraged David’s Quirkless daughter Melissa Shield toward support engineering. His American tenure forged his heroic identity, echoed in moves like "Detroit Smash" and "United States of Smash," and his ambition to be a global Symbol of Peace. Returning to Japan, his exploits slashed crime rates below 6%, securing his status as the unrivaled Symbol of Peace. He later partnered with persistent sidekick Mirai Sasaki (Sir Nighteye), leveraging Nighteye’s foresight Quirk for strategy. Years afterward, a covert battle seemingly defeated All For One but cost Toshinori his stomach and respiratory organs, restricting One For All to fleeting bursts. To preserve public hope, he hid his emaciated, blood-coughing form and defied Nighteye’s retirement pleas. Seeking a successor, he met Quirkless Izuku Midoriya, who endangered himself to save another. Recognizing Izuku’s selflessness and mirror of his past, Toshinori designated him One For All’s ninth holder. He trained Izuku physically, then joined U.A. as a teacher for him and Class 1-A. Though prioritizing student safety, his initial teaching overestimated their capabilities due to his own One For All mastery. He mediated complex dynamics like the rivalry between Izuku and Katsuki Bakugo. Toshinori’s ultimate fight against All For One unfolded in the "Final War" arc. Piloting the "Armored All Might" suit, he coordinated U.A. students and vigilante Stain to stall the villain. The armor shattered, crushing his legs. Paralyzed and near death, Katsuki and Izuku rescued him. Wheelchair-bound afterward, he sustained his optimism. Eight years later, he regained mobility, though shadows lingered in his eyes like his prime’s remnants. Retired, he guided Izuku and fellow heroes. His unwavering optimism, self-sacrifice, and dedication to saving lives and hearts defined every era. Nana Shimura’s taught smile symbolized his commitment to calm others despite personal fears. After passing One For All to Izuku, he stressed that true heroism sparks collective hope, not solitary burdens.