In a world where monsters once bred by the Demon King roam freely, a legendary witch named Lingreen is said to have subjugated these creatures long ago. Her descendant, a young girl named Leen, has inherited this rare and extraordinary ability to tame any monster. When a veteran adventurer and renowned witch hunter named Hakura finds himself nearly killed in a fight with a deadly hydra, Leen appears and saves his life. Now indebted to this unscrupulous and headstrong monstermancer, Hakura agrees to become her bodyguard, and the unlikely pair sets out to travel together.

Leen is a confident, selfish, and somewhat troublesome young woman, described as a little devil witch who is difficult to ignore. Hakura, by contrast, is an experienced and grizzled adventurer. Their relationship is immediately defined by constant bickering and arguing as they journey across the land. Despite their differences, they are bound by circumstance and an emerging mystery: what has truly drawn them together?

As they travel, the duo finds themselves embroiled in numerous troublesome incidents. While these problems often involve dangerous monsters, they soon discover that the root cause is not always the creatures themselves. Time and again, the interference, greed, and malice of humans prove to be the real source of conflict, leading Leen to lament how little she understands people. The narrative follows their journey through a world where it is never immediately clear whether the monster or the human is the true villain, forcing the heir to the monstermancer legacy to navigate threats from all sides.