Mitsui Yuuichi

An average college student.

Currently living alone in order to attend college. He doesn't have a girlfriend. ...Or rather, he's a siscon who just loves his little sister very, very much. Yet he cannot meet her, and even if he did, he's not sure if he could realize his love for her.

Then, not only does his sister suddenly appeared, but he also has to live together with her. His emotions and rational mind are easily thrown off the rails.