With her husband suffering from erectile dysfunction, Ruisa and her spouse visit a hot spring advertised as restoring virility, also bringing his father along for recuperation. The water does nothing for her husband—but works far too well on her father-in-law. When the unwanted erection refuses to subside, Ruisa gently relieves him under the pretense of caregiving. Once revived, however, his cock will not calm down, especially with Ruisa looking beautiful in her yukata. Their trapped desire soon collides with overwhelming force.