Kotaro Koizumi has two younger brothers, Shinjiro Koizumi, and Yoshinaga Miyamoto, who was not born at the time of his parents' divorce in 1982. Junichiro Koizumi was awarded custody of Kotaro and Shinjiro while Kayoko Miyamoto was awarded custody of Yoshinaga. He went on to Kanto Gakuin Mutsuura Junior High School and High School, but did not enter Kanto Gakuin University. Kotaro attended Nihon University School of Economics, but dropped out. Japanese press reports say that one of Junichiro Koizumi's sisters raised Kotaro and Shinjiro. Kotaro got his own weekly show on Fuji TV called "Kōtarō ga Yuku" (Kotaro Goes). He has also acted in TV dramas.