Hi! This is a stretch but I'm looking for a certain QT book, hetro, with a male yandere 

I've searched everywhere but I still can't find it, so maybe I'd thought trying my luck here

1 arc I remember goes something like this;

FL transmigrates right into her confession to the school Prince. The school Price is actually a serial killer and he agrees to her confession so he has a new victim (?). ML falls for her but when finds out that she knows abt his killings, he induces amnesia onto her. However she rmbs still but decides to act amnesiac. 

another arc: (maybe not from the same book im beginning to suspect) 

FL needs to reduce ML's blackening, so she returns back in time (20 years?) to teach him the ways of being a functioning member of society. She becomes his white moonlight and disappears after his blackening value decreases. But her disappearance in turn, increase the value. 

If you or anyone knows, please drop the title  much gratitude