A prelude to Marmalade Boy the TV series. Yuu remembers the day when his parents decided to divorce each other and remarry with another married couple. Toubled by the news, Yuu decides to take a walk, on which he spots a girl he falls in love with at first sight. He decides to follow this unaware girl and falls more in love with her. However he discovers who the girl really is...she's the daughter of his parents' new lovers.
Ambientato a cavallo tra il primo e il secondo episodio, Yū viene a sapere dei suoi genitori del futuro scambio di coppie e della figlia dei loro partner, che casualmente vedrà il giorno stesso.
La película se centra en el personaje de Yuu y en cómo persigue durante todo el día a Miki sin que ella ni Meiko, que está con ella, se den cuenta. Yuu se interesa por Miki, una niña que se muestra alegre y natural, impulsiva y dulce.
