Makihara Mana gets invited by her Father-in-law to visit the countryside and stay in the hot springs inn that the family is running. Because he needs help before the holiday season starts. Mana husband has to stay in Tokyo for work and so Mana-chan goes to the inn alone first.
The Father-in-law doesn’t have bad intentions at first but two things compound. First, her wife passed away a few years ago, and he hasn’t been with a woman since. Second, Mana-chan is a total hottie, and one day, purely by mistake, he saw her naked at the pool. And that ignited some old memories, thus paying her a visit overnight.
On the next scene, Mana’s husband arrives at the inn from Tokyo and they even have sex and the pool. But that conventional marital sex thing doesn’t work for Mana-chan anymore. Now she has a thing for Daddy.