Holy shit for the love of ballet-dancing jesus JUST KILL THE THOT!! but not before fucking her right in the pussy and showing her who's boss of course.
I try to not say this about horror but, holy fuck, this really, REALLY sounds like an edgy teenagers "this is my torture fantasy where i kill the evil prep sluts"
This has 40 more chapters...
I gave up and read the ending, mild spoiler (click at your own risk, I've tried to not spoil too much though):
Don't hold your hopes up, the story continues in the same manner for most of the remaining chapters, but the MC's acting career is short lived. This doesn't really matter since it's more of the same with more sadism. Eventually the MC gets his "happy end" in a rather anti-climatic way.
@Criver Tell me please, does she die, does she go to jail, do any of the other girls die by her hand? If I know that, I can finally drop this, since it is making my stomach ache, every time I even remember this manga.
She suicides in jail. MC finds out she's messed with all the women he's had a relationship with before that though, and gets tazed after he flips, so his friend has to save him. Eventually she tries to kill the middle school girl but MC grows some balls and protects her, police arrives and Midou gets jailed. Several years later we are shown the MC living happily with the middle school girl who is now pregnant.