Koto is a lone adventurer who rejects relying on others. One rainy day, he meets Milly — a healer girl who was expelled from her adventurer party for being “useless.” Although Koto intends to ignore her, Milly clings and ends up being taken in. As Koto starts training her, Milly unexpectedly changes class into the strongest one. But there’s something odd about Milly’s behavior… Together, they venture into dungeons in this somewhat clumsy, cute joint-life fantasy!