When Miki Koishikawa welcomes her parents home from their trip to Hawaii, the last thing she expects is for them to gleefully announce that they are getting a divorce. To her shock, they plan to switch partners with another couple they met on vacation. Barely able to keep her emotions in check, Miki begrudgingly attends dinner to meet the other couple and their strikingly handsome son, Yuu Matsuura.

After moving into a spacious house with her newly blended family, Miki struggles to adjust to her new lifestyle and her blooming feelings for Yuu. She attempts to navigate the coming school year with the help of her best friend, Meiko Akizuki, who is hiding a scandalous relationship of her own. However, the road ahead is not simple, as both Miki and Yuu have other potential suitors and emotional baggage from their pasts they are reluctant to reveal.