Historia
There has to be a catch when a deluxe rental property is this cheap–and this one connects to a perilous dungeon in another world! Far from being dissuaded, Touru jumps at the chance to sign the lease, hoping to go from high school dropout to big-time adventurer. He soon encounters a stranded knight: a gorgeous young woman named Ria. Touru rescues her and takes her back to Earth, where she promptly mistakes him for a Great Sage, seeing normal things like running water for evidence of his powerful magic.
Sinopsis vía AniList (en inglés).