The school romantic comedy revolves around a second-year high school student named Sorata Kanda who lives in Sakurasou, the dormitory for problem children at Sorata's school. One day, Mashiro Shiina - a cute girl who happens to be also a cosmopolitan, brilliant artist - moves into Sakurasou.
Sorata thinks to himself that he should protect Mashiro from the weirdos at Sakurasou, but Mashiro has a surprising secret: she has no idea how to take care of herself. She gets lost if she goes out, and her room is a complete mess. Sorata's dorm mates designate him as the "master" of Mashiro, and thus, an ordinary boy and a brilliant girl must live like "a master and his pet."