D.C. Girl's Symphony Pocket

On Hatsune Island the cherry blossoms bloom year-round without withering.
On that island lives Kojou Shio, a high school student. Her parents are abroad on business, so she lives with her step-brother, Takaaki.
One day, twin brothers, Ryouhei and Kouhei, and their older brother, Aoi, transfer to her school. All girl students are excited to see their handsome faces. So is Shio, but her first impression towards Ryouhei is very bad. Their school life starts like this... A while later, Shio decides to hire a home tutor. However, the home tutor is Kei, an older brother of Ryouhei, Kouhei, and Aoi....