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!