Kyousuke Irie is the head doctor of the Irie Clinic in Hinamizawa, serving as a key medical figure in the story. He grew up in poverty with a strong aspiration to become a doctor, and was known in his neighborhood as Doctor Kyousuke-kun from a young age. After training under a neurosurgery expert, he became involved in psychosurgery, a controversial practice. He performed lobotomies without patient consent, which led to him being ostracized from mainstream medicine. Believing that people who commit evil acts suffer from brain diseases, he was drawn to the Hinamizawa Syndrome research project. Recruited by Miyo Takano, he was sent to Hinamizawa to operate the clinic and study the syndrome. Through dissecting a live specimen, he developed an experimental cure for Hinamizawa Syndrome. He tested this cure on the terminally ill Satoko Houjou in order to avoid being forced to dissect her; the treatment succeeded, though Satoko requires daily injections and regular checkups. Eventually, the Tokyo government restructured and ordered him to end his research within three years.

Outwardly, Kyousuke is cheerful and highly respected in the community, known for making house calls and genuinely caring about everyone's health. He manages the Hinamizawa Fighters little league baseball team in his spare time. He has a pronounced maid fetish, which he expresses in playful, half-joking comments about marrying Satoko when she is older and chasing Rika Furude when she wears an Angel Mort waitress uniform. Behind this lighthearted demeanor lies a complicated past and a deep desire for redemption. His primary motivation is to prove his theory about brain disease and to make amends for his earlier unethical work. He works under Takano, unaware of her true, destructive plans, and is genuinely focused on finding a cure for the syndrome.

His key relationships include his professional collaboration with Miyo Takano, toward whom he is loyal but unaware of her ulterior motives; his caring, almost paternal bond with Satoko Houjou, for whom he has expressed interest in adopting; and his friendly interactions with Rika and the other children. Over the course of the story, Kyousuke develops from a seemingly harmless doctor with eccentric hobbies into a morally complex figure whose past mistakes drive him to protect Satoko and oppose the larger conspiracy once he learns the truth. His notable abilities are his medical expertise, particularly in neurosurgery and psychosurgery, his successful creation of a working cure for Hinamizawa Syndrome, and his dedication as a baseball coach.