After I Heard That After My Death, My Boyfriend Suddenly Realized That He Was Crazy

Looking for a Supernatural Novel with No Harem and an Unsystematic Protagonist Who Kills Decisively

I hope the protagonist is the kind of person who attaches great importance to love and righteousness. He doesn't want to be too holy. He is decisive in killing. If he likes someone, he will stay with him. He doesn't want a harem.