Black Kanojo 

A very mediocre junior high school sophomore Teru Hoshino was bullied by Amamiya, his childhood friend and famous at school for her big breasts. Despite the playful bullying now, his life has been fairly normal as far as he remembers. However, things start to change disturbingly, with Amamiya that not even he understands and his normal everyday life takes a dark turn that he never expected.