An ordinary high schooler, Kobeni Yonomori, learns out of nowhere that she's engaged to Hakuya Mitsumine, a boy she's never met, after a family arrangement neither of them had any say in. When Hakuya moves in from the countryside bringing his quietly odd little sister Mashiro along, the two households collapse into one under a single roof, with Kobeni's overprotective older sister Benio hovering over every awkward step toward acting like an actual couple. Told in four-panel strips, the manga plays the four of them adjusting to sudden family life for comedy rather than romance drama.