Hikaru Miyanishi is a tomboyish older sister who always confidently asserts herself. From childhood, she was athletic and consistently outperformed her younger brother. Suddenly, she receives a marriage proposal, throwing the entire family into disarray. The arrangement progresses smoothly, and soon she will be leaving home. Around the same time, the brother secures a job, prompting their mother to celebrate their independence with a long-overdue family trip to a hot spring resort, funded by her savings. It's a small gift to honor her children's coming of age. Unaware of the underlying emotions, the mother doesn't realize the secret feelings Hikaru harbors, or the brother's conflicted desires. Quietly, the family's final two-day, one-night journey begins.