Vulcan

Grotesquely fat and roughly as large as a small building, Vulcan was a demon of red skin set with three glowing red eyes, a mouth crowded with teeth and jutting lower fangs, and four horns split into a white pair and a gray pair. He clothed himself in nothing more than a scrap of white loincloth and hefted a giant brown club, which later turned out to be a branch taken from the World Tree.

Rated at S-Rank among magic beasts, Vulcan posed a serious threat. Sheer physical power let him hold Jinwoo down under a rain of blows, and for all his blubbery bulk he moved quickly enough that Jinwoo could not get clear of his strikes in time. Punishment barely fazed him too; he came away all but unhurt after a single punch hurled him crashing through a row of buildings. His Rage skill lifted his pain threshold and swelled each of his stats by half, running with no fixed cap on its duration.

Posted on the fiftieth floor, Vulcan marked the second great barrier Jinwoo had to break through while scaling the Demon Castle. His defeat scattered coveted spoils: the Demon Sovereign's Earrings, a World Tree Fragment prized as crafting stock, and the Orb of Avarice. A bleak note from the novel underscores his nature: too inept to make Bloodstone, the delicacy reserved for demon nobility, Vulcan ate more of his own kin than any other noble. The opening of the anime's second season also features a fight setting him against the Korean S-Ranks.