Kyou Mekui is a high school student who tends to skip school due to a trauma in his past. Kyou secretly creates songs using vocal song synthesis software as his hobby. Three girls who just entered fifth grade — the crybaby Jun "Jun-tan" Gotou, the strong-willed Nozomi "Zomi" Momijidani, and the somewhat sleepy Sora "Kuu" Kaneshiro who takes life at her own pace — email Kyou. These three girls, who were raised together like sisters since childhood, want Kyou to help them break into music.
Summary taken from: MyAnimeList