I tried to find all the information about his past, but it wasn't even hinted at in the manga. Unfortunately, the author di...

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— He found you /human version.

— The obsession never left him/ human

— He is jealous ~

— A sense of obsession takes hold of morality —

— You're his personal toy now

— From hate to love

— Even a virus won't calm the hatred between you

— you fell into a well

— your silent obsessive admirer