Yuri and her son live together. One day, to celebrate his university acceptance, she asks him what he wants. He confesses his desire—to have sex with her. Reluctantly, Yuri gives in. "Just once... you promise?" she says, though the words don't reflect her true feelings. They make love. After that, nothing happens between them again—until one day, Masaki suggests a hot spring trip as a final mother-and-son memory. Yuri happily agrees, yet she can't shake the feeling that something is about to begin.