Arata returned to his hometown due to his father’s work and was reunited with his three osananajimis after 10 years apart. They were the cheerful and innocent Yuuka, the reliable ‘onee-san’ Ayami and the once-small Mikana who had now grown to be very beautiful. Adding another osananajimi Yuusuke and his moodmaker imouto Mahiru, his school life is full of enjoyment like in the past. Then they received a strange e-mail inviting them to play a game. If they did not accept it, they will lose something precious.