The ml is not a serial killer but a psychopath with killing desires. Kirin tried to get into his club because the members raped his sister and he ends up with ml. I think at the end of the story they are together for like a decade or more.
Ohh, okay. Now I'm starting to remember more of it..Thanks for your response ^_^
*spoiler*
So did he actually kill the guys that raped Kirin's sister? I vaguely remember at least one (or more) person (or people) getting killed.
The other guy he got in a relationship, the psychopath, killed most of this guys and also lured the last one in a trap, but Kirin was the one who killed him in the end to get his revenge.
It's been a long time since I've read this, and I'm trying to remember what it's about. Is the ML a serial killer?