Mizuhara Tsuzumi

A mysterious girl that transfers into Mitsuki's class. She seems completely ignorant about the most ordinary of things, constantly asking others for advice. She moves into the dormitory where Mituski lives, and starts a habit of barging into his room without asking, usually through a window.
Tsuzumi absolutely loves ice cream and enjoys it in every chance she gets.

Spoiler

Tsuzumi is actually a non-human sent on a mission to capture a wanted man.