There aren't too many games banned from Twitch, but usually it's those with a malice behind violence or extensive nudity. Games like Hatred and BMX XXX if you will. Well, now we can throw Yandare Simulator on to that short pile.
The game is in an anime style and has the player take up the role of a school girl obsessed with a particular boy, having you murder any girl who shows interest in him, hiding them from the police and appearing innocent to other students. The game went viral on YouTube and Twitch, but it seems in the latter's case, its days are over.
Honestly, I've seen it played, and it's actually fairly innocuous and silly on the violence side, despite the concept sounding so ghoulish, especially when compared to things like Mortal Kombat X. This leads me to believe this might well be motivated by some of the unsavoury sexual themes that are hinted at or just the fact you are murdering innocent school children. Actually… when written down like that, it might make some sense, but Twitch haven't outlined why the ban has been put in place, so this is all speculation.