Kyōsuke Irie is the head doctor of the Irie Clinic, the only medical facility in the village of Hinamizawa. In addition to his medical duties, he serves as the coach of the local youth baseball team, the Hinamizawa Fighters, and is affectionately referred to as “Kantoku” by the children. He presents himself as a calm, well‑spoken, and intelligent adult, and his earnest bedside manner has earned him the trust of villagers across all age groups. He also acts as the personal physician for the Sonozaki family, including the formidable family head Oryō.

Behind his composed exterior, Irie carries a complicated past. Before coming to Hinamizawa, he was a promising neurosurgeon who specialized in psychosurgery, a controversial practice that involved procedures such as prefrontal lobotomies. When public opinion turned against such methods, he was ostracized from the medical establishment. Seeking a chance at redemption, he was recruited by Miyo Takano to research the mysterious Hinamizawa Syndrome, a neurological disorder endemic to the village. With backing from an organization known only as Tokyo, Irie established the Irie Institute to study the syndrome. He succeeded in developing both a treatment and a preventive medication, though a complete cure remains elusive.

Irie’s motivations are twofold: atonement for his earlier medical work and a sincere desire to help the people of Hinamizawa. He is particularly invested in the well‑being of the Hōjō siblings, Satoshi and Satoko. He worries about Satoshi, who once protected Satoko from their abusive aunt, and he is deeply attached to Satoko, even considering adopting her. He administers regular treatments to Satoko, who suffers from the syndrome, and cooperates with Rika Furude, who is aware of the underlying conspiracy. Despite his good intentions, Irie often finds himself caught in the tragic cycles of the story; in many worlds he is either killed or forced into a coerced suicide as part of the larger plot.

One notable eccentricity is his overpowering obsession with maid costumes. When excited by the subject, he sheds his usual restraint and becomes animated, sometimes to the point of comical excess. This quirk does not diminish the respect he commands, but it provides a contrast to his otherwise serious demeanor.

Irie is a skilled physician and researcher, but he is not a combatant. He holds the rank of Second Lieutenant in the Japan Self‑Defense Forces due to the military connections of the research project, though he dislikes being addressed by that title and considers himself purely a doctor and scientist. His role in the story is that of a well‑meaning supporter who holds critical knowledge about the syndrome and its treatment, yet he is often manipulated by those with more ruthless agendas. His development across the arcs shows a man wrestling with his past mistakes, striving to protect the children he has come to care for, and ultimately seeking to break the cycle of tragedy through his medical expertise.