When Miki Koishikawa greets her parents upon their return from Hawaii, she least expects them to joyfully declare their intention to divorce. To her astonishment, they intend to swap partners with another couple they encountered during their holiday. Struggling to maintain her composure, Miki reluctantly joins them for dinner to meet the other couple and their notably handsome son, Yuu Matsuura. Following her move into a large home with her newly formed blended family, Miki finds it difficult to adapt to her changed circumstances and her growing affection for Yuu. She tries to manage the upcoming school year with support from her best friend, Meiko Akizuki, who is concealing a scandalous romance of her own. Yet, the path forward is complicated, as both Miki and Yuu face interest from other potential suitors and carry emotional baggage from their pasts that they are hesitant to disclose.