Maiku Kamishiro's past has always been somewhat of a mystery to him. The only clue he has to who is family might be is an old photograph showing two young children, a boy and a girl, playing in a small pool outside of a blue house. In an attempt to find his family, he moves to this blue house and begins working as a programmer. He's living a comfortable life until the day two very different girls show up at his door, both in possession of the same photograph, and both claiming to be his twin. With no way to prove who is a relative and who is a stranger, Maiku allows both girls to move in with him until he can know for sure which one is his twin.