Not so sure I'd consider her yandere quite yet, though. Obsessive, sure, but I don't quite see the violence yet. So far she's managed to manipulate him well enough without that, and there have been no rivals to spark such behavior either. Not ruling out the possibility either, though, should circumstances change. It'll depend on how she decides to solve her problems then.
Rules of Inseki hentai
1. Fuck her... Hard.
2. If she's not addicted to your cock yet, fuck her harder
3. If it still hasn't happened, try getting kinkier. Spanking and whatnot.
4. If she STILL isn't addicted, you're clearly not doing it right.
"What's worse is she has an unhealthy obsession with me"?
Worse? Clearly you meant better, yes?
Still, I guess it was only a matter of time before he snapped, the way she kept coming onto him. And in the end, all it took was for him to find her in the male bathroom and have two other guys...very coincidentally becoming accidental wingmen by coming into the toilet.
That ending though. Well...I'd certainly like to see more of them living together while their parents are...not around...