The long-running duo of Yajima Junko and Shinokita Reiko, two fiercely strong high school girls known for solving mysteries and fighting corruption as they transfer between schools, find themselves swept into a fantasy realm. One day while walking through a busy street, the pair is suddenly engulfed by a mysterious magic circle and transported to an unknown world. At nearly the same moment, three of their close allies—the charismatic Tokunari Yukiya, the skilled Koga ninja Kotetsu, and the regal Takakura Takako—are also summoned to the same world by the prince of the kingdom of Cherarat.

However, the two groups arrive under very different circumstances and on opposing sides of a growing conflict. Yukiya, Takako, and Kotetsu are deliberately summoned by the human royal court and assigned heroic roles suited to their talents: Yukiya as a brave warrior, Takako as a holy maiden or sage, and Kotetsu as a wise strategist. Meanwhile, Yaji and Kita are summoned not by humans but by the forces of darkness, pulled through a dark gate by demons. In a comedic twist on classic isekai tropes, Junko Yaji is assigned the role of the Demon King, while the more level-headed Reiko Kita is given the entirely improvised job of Stopper, a role clearly meant to keep her impulsive partner from causing too much chaos. Despite her fearsome title, Yaji remains her usual brash and justice-driven self, showing no desire to conquer the human world. As the adventuring pair, they befriend creatures like a talking owl and a dog in clothing while defending frontier villages from monsters.

The core narrative tension comes from this separation. The group summoned by the prince works to gather information about the land and the source of the monstrous threats, growing suspicious of their summoner's motives. The group in the demon realm fights on the front lines against magical beasts, dealing with territorial lords and political intrigue. Neither group is initially aware that their friends are in the same world, though the situation suggests their paths are destined to cross. Their ultimate goal is to find a way home while navigating the chaos of mistaken identities, political schemes, and the simple fact that Junko Yaji has been labeled the enemy of the kingdom that holds her friends.