Toshinori Yagi, also known by his hero name All Might, was born quirkless. He developed a conviction during his teenage years that the world needed a "Symbol of Peace" to inspire people and bring about an age of harmony, a goal he resolved to pursue. He was trained by the seventh user of One For All, Nana Shimura, who passed the Quirk to him. Following her death in a battle against All For One, Toshinori received further training from Gran Torino, his homeroom teacher at U.A. High School. After graduation, he traveled to the United States for training, where he met David Shield and his daughter Melissa. Upon returning to Japan, he launched his hero career, eventually rising to become the Symbol of Peace and the number one hero, drastically reducing Japan's crime rate. His heroic career was defined by a series of battles against the supervillain All For One. Their first major confrontation left All Might with critical injuries that destroyed his stomach and parts of his respiratory system. This wound permanently reduced his ability to use One For All, restricting him to three hours of hero work per day, a limit that gradually decreased over time. Nevertheless, he persisted in his hero duties for five years before initiating a search for a successor. He eventually accepted a teaching position at U.A. High School to aid in this endeavor. It was during this period that he met Izuku Midoriya, a quirkless young boy. Initially, Toshinori advised Midoriya to be realistic about his dream of becoming a hero. However, after witnessing Midoriya’s selfless bravery in attempting to save Katsuki Bakugo from a villain, Toshinori recognized him as a worthy successor. He passed One For All to Midoriya and committed himself to training the boy, who was later accepted into U.A. High School. As a teacher and mentor, Toshinori continued to confront villains while hiding his weakened condition from the public to preserve morale. His time as a hero reached its climax in a final battle against All For One during the Kamino Ward incident. He expended the last embers of One For All to defeat his nemesis with the United States of Smash attack, an effort that left him entirely powerless and compelled his retirement. After retiring, he dedicated himself fully to teaching and mentoring Izuku Midoriya. During the Final War, though quirkless, he confronted All For One once more using a high-tech armored suit named Armored All Might, developed with assistance from Melissa Shield. This suit was fitted with support items engineered to emulate the abilities of Class 1-A students. In the battle, his legs were crushed and the suit was destroyed, leaving him confined to a wheelchair. He was later rescued from death by Katsuki Bakugo and Izuku Midoriya. In the aftermath, eight years later, Toshinori Yagi had gained more wrinkles but recovered the ability to walk. His eyes also reverted to having white sclerae, as they had been in his youth. Toshinori Yagi possesses two distinct forms. His empowered "muscle form" is a towering, immensely muscular figure approximately 220 cm tall, with a powerful build, short blonde hair, and striking blue eyes. His classic hero costume consists of a skin-tight blue bodysuit with a red and white design, a gold belt, and gold boots. His true form, a consequence of his injuries, is severely emaciated and skeletal, with long limbs, a pronounced neck, and sharp facial features. He has wavy blonde hair with two long strands framing his face, no eyebrows, and black sclerae in his eyes. A large scar covers the left side of his chest, and he frequently coughs up blood due to his damaged respiratory system. After retirement, he stopped wearing baggy clothes and adopted attire suited to his true form. His personality is dual-natured. As All Might, his hero persona is exuberant, dramatic, and charismatic, drawing from Western superhero archetypes. He consistently operates with a giant smile to inspire hope and reassure others, a principle instilled in him by Nana Shimura. In his true form as Toshinori Yagi, he becomes reserved, solemn, and avoids attention. Core traits that endure in both forms are his optimism and a certain oafishness. He exhibits a powerful sense of self-sacrifice, invariably prioritizing the safety of others over his own well-being and personal life. He is highly intelligent and perceptive despite his theatrical hero image, with sharp tactical abilities in combat. He formerly possessed the transferable Quirk One For All, which stockpiles immense power and enhances all physical capabilities to superhuman levels. This granted him tremendous strength, enabling him to alter weather patterns and demolish city blocks with wind pressure from his punches; immense speed, allowing movement faster than the eye can follow; near-invulnerability; and immense stamina. His signature attacks are all named "Smashes," such as Detroit Smash, Texas Smash, and his ultimate technique, United States of Smash. After passing One For All to his successor and expending its last remnants in his final battle, he lost the Quirk completely. However, a vestige of his consciousness endures within the Quirk factor, permitting a psychic connection with its current holder. Even without a Quirk, he maintains sharp reflexes, keen intuition, and an indomitable will.