Adult PC Game: Kara no Shoujo by Innocent Grey Archive

The year is 1956; a series of bizarre murders rocks the city of Tokyo.
Tokisaka Reiji, an ex-cop turned private eye, joins the investigation at the behest of his friend Uozumi Kyozo, a detective in the MPD.
At the same time, he takes on a missing persons' case at a private all-girls high school, as well as a mysterious request from a girl named Toko to find her true self.
As Reiji frantically struggles to crack the case, he learns that the murders bear an uncanny resemblance to a case in which his own fiancé was murdered six years ago.
But try as he might, the body count just keeps rising...