Morisaki Yuuta moved into the city after his mother's death with his older sister; Ruri and attended the same highschool. In the school corridor, he bumped into a student in the name of Kusunose Hina who participates in the Tennis Club. From that moment onward, Yuuta remembered his childhood promise he made to the girl whom he used to play with when his mother was still alive.

[From ANN]