Heaven Canceller, nicknamed the "Frog-Faced Doctor" for his distinctively frog-like features, is a highly skilled physician in Academy City. He presents with a bald head and grey hair, typically dressed in a doctor's outfit with a stethoscope, and humorously acknowledges his nickname with an ID card bearing a frog sticker.

Profoundly compassionate and principled, he adheres strictly to the Hippocratic Oath. Patient well-being is his paramount concern, regardless of affiliation or morality, and he deeply values being relied upon. This commitment persists despite his acknowledged exposure to Academy City's darkness, having witnessed "more blood and tears" than most. He fiercely opposes endangering patients, confronting even Academy City's ruler, Aleister Crowley, warning against manipulating those under his care. Their relationship is complex, rooted in shared history but strained by ideology; Heaven Canceller refrains from harming Aleister, still viewing him as a patient. He similarly opposes unethical researchers like Kihara Gensei, whose methods disregard human suffering.

His background includes pivotal contributions to Academy City's founding. He first encountered a near-death Aleister Crowley, pursued by the Magic Side, in a small English village. After saving Aleister, he conceived the idea for Academy City and assisted in establishing it in Japan, choosing to remain a practicing doctor rather than take a leadership role. Despite this, he retains significant authority. He developed the life-support system sustaining Aleister's longevity but later abandoned further life-extension research, including the Dark Legacy project.

Medically, he demonstrates unparalleled expertise, capable of curing terminal illnesses and healing near-fatal injuries under his philosophy: "as long as you don’t die, I can save you." His limitations involve brain traumas, such as Kamijou Touma’s memory loss or Accelerator’s impaired calculation abilities. However, he devised a solution for Accelerator by configuring the Misaka Network to compensate for the damage, allowing Accelerator to retain his powers.

He frequently treats central characters. He reattached Touma's severed arm and expressed frustration over his inability to restore Touma's memories. During the Academy City Invasion, he sheltered Index and a wounded Hound Dog member, coordinating with Accelerator to protect Last Order, emphasizing survival as a prerequisite for healing. He later confronted Aleister about endangering patients. His interventions include saving Yoshikawa Kikyou after a gunshot wound, noting Accelerator’s unconscious control of her blood flow during surgery. He also oversaw Last Order’s recovery and release post-invasion.

In the Skill-Out Uprising and Battle Royale arcs, he reassured Last Order about Accelerator’s return and was later confronted by Accelerator demanding designs for his electrode device. His operational base is a hospital where he manages routine and critical cases, maintaining vigilance over his patients' long-term well-being even after discharge.