Chii-chan

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

(Source: Kodansha USA)

Note: Prequel spin-off of the movie Poison Girl (Doku Musume).