Proof of a Substitute

[Family curse + anime elements + mystery + a century of history (partly based on real references) + real-world setting + (from Chapter 42 onward) two male leads + conceptual deity] Detective Nakamura Kihara wakes on a stormy night to find a bloodstained kitchen knife in his hand and a corpse lying in front of him that looks exactly like himself. Every piece of evidence in the police investigation points to him as the killer, but he is certain he has been framed. As he digs deeper, he gradually discovers that he is actually his late colleague, Takahashi Akira. In the end, amid a web of illusions and desires, he sees the truth: he is both the killer and the victim. After his death, the ninety-year-old Yuki family receives its only two young guests in sixty years. Their investigation brings the brutal truth to light: a century-long conspiracy between the upper echelons of the military, politics, and the medical system.

A warning!!!!! If you like fast-paced stories, I recommend starting from Chapter Eight. The beginning is all setup and moves very slowly!!! Please don't give up on this story, I beg you~