After hurting his back, an old man gets fired from his job as a blacksmith for a mercenary group. He sets up a small weapons shop in town and in search of workers, he hires a quiet and earnest girl named Relm. However, in reality, she's a tomboyish half-succubus who's too honest about her sexual desires! In exchange for helping out at the shop, Relm asks for a "reward". For her, that reward is "essence", which is essential for survival.
This is a slutty sex comedy fantasy revolving around such ''rewards''.