Chii-chan

Yuua Hayakawa used to love playing with Chii, a mysterious girl with a murky family life who likes collecting dead insects, but it's been years since they've spoken. Now, Chii hardly ever even comes to school. One day, Chii shows up to class in beat-up gym clothes with a handful of dead bugs and starts a commotion that gives Yuua's classmate, golden boy Koudai, an idea: he's going to save Chii, and he needs Yuua's help to do it. But clean-cut exteriors don't always promise good intentions, and the darkness in Chii may be more dangerous than Yuua had ever imagined.

(Source: Kodansha USA)