The world is a dark place where demons lurk and the "Unmeasured Realm" spreads. Strangely enough, the only effective means of exorcising the darkness and cultivating human lands is to "draw a map". One day, a young pioneer, Zaba, meets a beastman girl, Rita, in a cave in the Unmeasured Realm. Guided by her ability to instantly survey and map with her excellent hearing and the strong will that resides in her slave body, Zaba proposes to accompany her to the frontier. The possibility of saving people from being turned into demons lies in the abandoned city of Amstelm...!