Yamato looks like a typical guy, but being surrounded by one older sister and two little sisters, he greatly loves his sisters a lot. One day, his older sister Azusa informed that he will be transferring to a girl's boarding school as part of a test case for coeducation initiative. He also has to help the school board chairman's daughter Yurika with various duties. Reluctantly he heads to school and waiting there was his little sisters Aoi and Akane who lived apart from him, as well as his childhood friend Ena who’s like family to him. His little sisters shower him with pent-up love, having not seen their older brother for so long.