In Marmalade Boy, Miki Koishikawa's world is shaken when her parents return from Hawaii and reveal their plan to divorce and swap partners with another couple they met there. Reluctantly, Miki attends a dinner to meet the new family, where she comes across Yuu Matsuura, the charming son of the other couple. As Miki adapts to life in a larger household with her newly blended family, she starts to develop romantic feelings for Yuu. With the support of her best friend, Meiko Akizuki, who is keeping her own secret relationship hidden, Miki tries to manage the challenges of the upcoming school year. However, their path grows more complicated with other potential love interests for both Miki and Yuu, along with lingering hidden emotions from their pasts that they are hesitant to confront.