Heaven Canceller, nicknamed the "frog-faced doctor" for his distinct amphibian-like features, serves as a preeminent physician in Academy City. His bald head bears traces of grey hair, and he consistently dons medical attire. A frog sticker adorns his ID card, subtly acknowledging the comparison. Bound by an unshakeable dedication to the Hippocratic Oath, he treats every patient impartially, driven solely by their need for care and his desire to be trusted. This ethos often pits him against Academy City's shadowy factions, notably opposing Kihara Gensei’s unethical experiments. Beneath his compassionate demeanor lies a history steeped in witnessing profound darkness, leading him to claim he endured "a hell far worse" than others yet emerged unbroken. His defining creed remains: "Don't die. As long as you don't die, I can save you." Prior to Academy City’s inception, he discovered a dying Aleister Crowley in an English village, hunted by the Magic Side. After saving Aleister, he conceived the plan to establish Academy City in Japan. Though instrumental in its founding, he rejected a leadership position to remain a practicing doctor. Despite this, he wields significant influence, facilitating meetings between figures like Misaka Mikoto and incarcerated individuals. He also created and maintains Aleister’s life-support system but later abandoned research on life extension and the device known as Dark Legacy. His near-miraculous medical skills heal virtually any affliction except select brain conditions. He reattached Kamijou Touma’s severed arm and saved Yoshikawa Kikyou from a point-blank gunshot by utilizing Accelerator’s residual powers. When Accelerator’s brain damage impaired his abilities, Heaven Canceller integrated him with the Misaka Network to restore partial function. However, his inability to recover Touma’s lost memories haunted him. During the Academy City Invasion, he sheltered Index and others while coordinating with Accelerator to protect Last Order. He warned pursuing Hound Dog operatives to surrender, pledging to save them if they survived Accelerator’s retaliation. His rapport with Aleister fractured when he condemned endangering patients like Touma and Accelerator for Aleister’s schemes. Though Aleister severed ties, Heaven Canceller continued treating him as a patient, upholding his oath. Later, he supervised Last Order’s recuperation and supplied Accelerator with choker blueprints upon request. His hospital routinely treated pivotal individuals—including Touma (repeatedly), Accelerator, the Misaka Sisters, and GROUP members—cementing his role as a stabilizing pillar amid the city’s turmoil. He persisted in operating on critically injured patients, such as a gunshot-wounded Touma, even when his post-operative counsel was ignored by those rushing back into conflict.