Masamichi Yaga served as the principal of Tokyo Jujutsu High, holding the rank of grade 1 jujutsu sorcerer. He possessed a tall, muscular frame with tan skin, short spiky dark brown hair shaved on the sides, thick eyebrows, and a mustache and goatee. Sunglasses became a consistent part of his appearance, especially after becoming principal, complementing his formal black attire: a long-sleeved zipped jacket, pants, and shoes. Earlier, as a teacher, his hair featured two straight shaved lines and he wore sunglasses less often. His specialty lay in puppet jujutsu, creating and controlling cursed corpses—doll-like constructs infused with cursed energy. His most significant creation was Panda, an abrupt mutated cursed corpse housing three independent cores that granted sentience, self-sustaining cursed energy, and emotional capacity. Raised and trained by Yaga, Panda regarded him as a parent, a relationship known throughout the school. Yaga also developed other functional cursed corpses: combat-oriented Cathy, training-focused Tsukamoto, and Takeru—a dog-like creation made using soul information to comfort Kusakabe's sister after her son's death. Panda's creation triggered jujutsu authorities to interrogate Yaga over fears he could mass-produce autonomous weapons. He subsequently hid his later creations within a forest shielded by Tengen, though he broke this secrecy to craft Takeru. As an educator, Yaga prioritized testing students' personal convictions, shaped by his former student Suguru Geto's betrayal. He dismissed externally motivated aspirations, initially disqualifying Yuji Itadori for citing his grandfather's dying wish. During their interview, he deployed Cathy to pressure Yuji into articulating self-determined reasons for becoming a sorcerer, asserting that sorcerers "die with regrets" and must internalize their purpose. Despite tradition, he advocated for leniency towards potentially valuable sorcerers like Yuji and Yuta Okkotsu when higher-ups demanded execution. His teaching included disciplining problematic students, physically punishing Satoru Gojo for mission negligence and mediating conflicts between young Gojo and Geto. Though often exasperated by Gojo's antics, Yaga shared his progressive educational views, understood him deeply, and maintained a working relationship into adulthood. Yaga's past included mentoring Gojo, Geto, and Shoko Ieiri during their second year (2006). He assigned Gojo and Geto the Star Plasma Vessel escort mission, which catalyzed Geto's descent. Geto's subsequent massacre of a village and his parents devastated Yaga, who later refrained from blaming Gojo for failing to execute him. Twelve years later, Yaga participated in confronting Geto during the Night Parade of a Hundred Demons. After the Shibuya Incident, the jujutsu higher-ups sentenced Yaga to death, citing his responsibility for influencing Gojo and Geto while covertly seeking his cursed corpse techniques. Intercepted en route to visit Panda by Kyoto principal Yoshinobu Gakuganji and another sorcerer, Yaga refused to divulge his methods to avoid execution. He fought without his cursed corpses. Mortally wounded, he revealed the methodology to Gakuganji: embedding three mutually stabilizing cores into a corpse using replicated soul information, a three-month process to achieve self-sustaining energy. He framed this knowledge as "a curse from me to you" before dying in Panda's arms. Yaga harbored an unintentional fondness for cute objects, reflected in his cursed corpses' designs. His hobbies included collecting sunglasses and crafting dolls through felting. He disliked sweet liquor but favored smoked daikon pickles. He had been married once and was divorced at the time of his death.