Shinichirou was raised in an orphanage close to a clinic where his best childhood friend Kai Nanami's parents worked. He has two brothers, Soushi Asaka and Ryouya Kozuki. Shinichirou is the youngest one out of the three. He is a detective and a math teacher. He is also the husband to Nanami Kai. He becomes the big brother figure to Matsuri Honjou, Fujimori Sunao, and Sora Hashiba.