At 27 years old, Hayami is “the perfect sempai,” but at home she becomes a massive slob. It just so happens that her junior, Yamamoto-kun, is a pro at housework! Hayami takes him in as her wife, and over time, they go from being housemates to boyfriend and girlfriend. Now, they're celebrating Yamamoto-kun's birthday for the first time as a couple. Honoring her wife's request, the two go on a special birthday trip to the hot springs! But as much as Hayami's enjoying the vacation, she finds herself feeling unusually self-conscious… Get ready for a heart-pounding volume as the new couple takes their relationship to the next level!