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. After finding out Yamamoto-kun's got marriage on the brain, Hayami takes the plunge with a proposal! Things heat up even more when Hayami meets her mother-in-law-to-be, whose charms drive a massive wedge between the two lovebirds. But life doesn't end at "I do"; the two have a long and happy road ahead of them!