Dead man Switch
OMG, seriously think the Yandere guy is a regular person trapped in a horror game where MC is an important character that needs to make it to the "end" alive. In order for Yandere guy to finish the game. Also I think Yandere guy has been at it for a while going off the scars. Clearly Yandere guy has been "reset" many times. I think Yandere guy has an obsession with MC because MC is the only reoccurring and consistent person in the game and all Yandere guy really has keeping himself (somewhat) sane and hopeful. Also MC can also be Yandere guys type so yeah...
Amulet