Synopsis
Koizumi is an elderly military officer who first appears in the Matsuribayashi-hen arc of Higurashi no Naku Koro ni Kai, voiced by Yoku Shioya. He became close friends with Hifumi Takano during World War II, and once Hifumi began investigating what he called the Hinamizawa Syndrome, Koizumi used his connections to arrange a hearing before high-ranking officials so the research could secure funding.
Koizumi never attended that meeting himself, already suspecting how it would end: the officials dismissed Hifumi's thesis as delusional fiction and pressured him into abandoning the study. His absence was rooted in guilt rather than indifference, and the humiliation that followed haunted him for years afterward.
After Hifumi's suicide, Koizumi sought out his adopted granddaughter, Miyo Takano, whom he had known since her childhood. Impressed by her determination to continue her grandfather's work, he backed her financially and politically as an act of contrition, helping her gain a military commission and establish a laboratory disguised as the Irie Clinic — though this also drew the attention of the shadowy faction known as "Tokyo".
Koizumi's death, shortly before the story's present day, strips Miyo of her strongest protector and leaves her research at the mercy of officials eager to bury it quietly. The manga adaptation expands his role considerably, including a scene where he holds Miyo at gunpoint to test her resolve before pledging his full support. He is described as having brown hair and eyes and a moustache, usually seen in a black suit or a green shirt.
