Kouki is tasked by the Hanabishi family patriarch to spend the summer living with the four daughters and choose one of them as his bride to fulfill a long-standing promise between fathers. As he navigates his complex emotional and physical bonds with Yurina, Momone, Saori, and Anzu, Kouki struggles with the pressure to pick a single partner. Ultimately, realizing he loves all four sisters equally, he declares his intention to marry every one of them, even if it means changing the law.