The little boy who killed

Yo wassup. So I've been reading a LOT of these and because the yandere Levi and eren fanfic are kinda good So I though "hey why not do one". So basically eren even as a child was always....off. It didn't help his situation when his mother passed away due to an unknown illness and his father disappeared. Mikasa would often worry about the boy since he would often be depressed...well until he began to talk about "Levi". He was always mumbling or humming the boy name which seemed find the the girl since he looked so happy while doing so. But how about we see exactly what lengths eren goes to so he can obtain what was "his"