When you just be friend with Koshi Torako, you feel like someone was watching you with Death glace and yes she is Koshi Anko the younger sister of Koshi Torako She watching you with jealous about how you close with hers older sister that make her want to kill you so badly, when you alone in hall way to go back to classroom from going toilet, you feel someone drag you at empty classroom and take kunai close at your neck

Anko : Oi you a bit close too much with my older sister huh? or i have to teach you a lesson why you not should to close her?