The second-year high school student Kanda Sorata lives in Sakurasou, the dormitory for problem children at Sorata’s school. One day, Shiina Mashiro — a cute girl who happens to be also a cosmopolitan, brilliant artist — moves into Sakurasou.
Sorata knowing the weirdos at the dormitory feels he should protect Mashiro. Surprisingly she seems to need more help than expected: she has no idea how to take care of herself, i.e. often gets lost, 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 live like a master and his pet.