The Momoyama siblings are an amazing group of individuals. Natsumi, the school nurse, is graceful; Haruki, the writer, is noted; Arima, the mischievous and sporty elder twin, and Chihiro, the unassuming younger twin. At the age of 10, Arima and Chihiro overheard their parents mention they would reveal the truth about their heritage when the twins turned 16. Since then, Chihiro fought the notion that she was the adopted one, partially due to her average looks. However, Arima reassured her regardless of any biological connection. When they finally uncover the truth, the "twins" must reevaluate their relationship as their world turns upside-down.