Haruka has reunited with his classmates in the city of Omui, but as a loner through and through, it isn't long before their presence starts getting to him. An excursion to a dangerous underground dungeon gives him a much-needed reprieve...when he falls all the way to the bottom level, the domain of the legendary undead Emperor of the Labyrinth! But Haruka won't be alone for long—he'll soon be joined by a powerful skeleton knight who's somehow also a seventeen-year-old girl!