When Touru stumbles upon a suspiciously low-cost rental with a dangerous twist—a gateway to a treacherous dungeon in an alternate realm—he seizes the opportunity, envisioning a path from school dropout to esteemed adventurer. His new abode unexpectedly houses Ria, a stranded knight of striking beauty. After rescuing her and returning to Earth, Touru finds himself mistaken for a legendary Great Sage by Ria, who interprets mundane Earthly conveniences as manifestations of his formidable magic prowess. As Touru yearns for a heroic destiny, his immediate challenge lies in navigating the complexities of cohabitation with a charming girl from a world beyond.