As a bystander in class, Kazuhiko Nukumizu overhears popular girl Anna Yanami's heartbreak after being rejected by a guy who made a promise with her as a child. This rejection leads to a discussion among other overlooked heroines like Remon Yakishio and Chika Komari. Amidst the conversation, Nukumizu learns about the two types of girls: childhood friends and unfaithful partners. The tale of these 'losing heroines' begins, promising a mysterious and enlightening coming-of-age journey in Makeine.