Maiku Kamishiro's past has always remained somewhat of a mystery to him. The only clue he possesses regarding his family is an old photograph depicting two young children, a boy and a girl, playing in a small pool outside a blue house. In an effort to locate his family, he moves into this blue house and starts working as a programmer. He lives a comfortable life until the day two very different girls appear at his door, both holding the same photograph and both claiming to be his twin. With no way to determine who is a relative and who is a stranger, Maiku allows both girls to move in with him until they can be certain.