Toshinori Yagi, known as All Might, entered the world without a Quirk yet aspired to become a hero embodying hope and safety. As a teenager, he met Pro Hero Nana Shimura. Recognizing his determination, she became his mentor and passed the transferable Quirk "One For All" to him, making him its eighth holder. This Quirk stockpiles power from previous users, granting superhuman strength, speed, and durability. Following Nana Shimura's death at the hands of the villain All For One, Toshinori trained under her associate Gran Torino before moving to America to begin his hero career. There, he refined his heroic ideals and inspired future heroes like Cathleen Bate (Star and Stripe). Returning to Japan, he became the Symbol of Peace, reducing national crime rates to under 6% through his presence and actions. A pivotal battle with All For One left Toshinori severely injured, costing him his stomach and parts of his respiratory system. This forced him into a chronically weakened, emaciated state, which he concealed from the public to maintain morale. In this form, he appeared skeletal and frail, often coughing blood. Despite his injuries, he continued hero work but could only maintain his muscular "hero form" for limited periods, initially three hours daily, decreasing over time. His hero persona embodied classic superhero archetypes: exuberant, charismatic, and always reassuring civilians with his catchphrase, "I am here!" and a deliberate smile to project confidence. This contrasted with his true form's reserved and solemn demeanor. After encountering Izuku Midoriya, a Quirkless teenager demonstrating selfless bravery, Toshinori chose him as his successor and passed One For All to him. He joined U.A. High School as a teacher for Foundational Hero Studies to mentor Izuku and other students. Though enthusiastic, his initial inexperience led to overestimating students' capabilities, as his own mastery of One For All had come effortlessly. He prioritized instilling heroic values like self-sacrifice and optimism, facing challenges balancing instruction with his declining health and residual hero duties. During the Kamino Incident, Toshinori exhausted his remaining power to defeat All For One and rescue Katsuki Bakugo, publicly revealing his weakened state and retiring as a hero. He fully transferred One For All to Izuku, ending his era as the Symbol of Peace. He continued supporting hero society as a mentor and later U.A.'s vice principal. In the Final War against All For One and Tomura Shigaraki, he utilized a high-tech armored suit developed with Melissa Shield. This suit mimicked the abilities of Class 1-A students, allowing him to fight Quirkless. The suit was destroyed during the battle, and Toshinori sustained further injuries, including crushed legs, temporarily confining him to a wheelchair. Eight years post-war, he regained his ability to walk and remained at U.A., focusing on guiding new generations of heroes. His personality consistently blended optimism with a sense of responsibility, though he privately grappled with trauma from Nana Shimura's death, guilt over failing to protect her grandson (Tomura Shigaraki), and the societal collapse following his retirement. He believed heroes must save both lives and hearts, a principle he upheld even without powers.