Wataru Kaneda is a typical high school student who also happens to work as a part-time programmer. Starting his second year of school, Wataru naively thinks nothing unusual will happen so he can focus on his job instead. However, Wataru's ideal school life is abruptly interrupted by three girls: Tamayo Ougi, Rika Aikyou, and Sanae Mayuzumi—all of whom claim that one of them will become his fiancée according to a pact they made a decade ago.

To further complicate matters, the trio happens to move into the same apartment floor as Wataru, which irritates Tomo Kurebayashi, his childhood friend who also has feelings for him. As the girls demand his attention and final choice, Wataru must figure out what to do to resolve this predicament.