Reborn in another world as a demon lord, Yuki is off on another adventure. This time, he's taking part in a dungeon conquest at Nell's invitation. He heads to their destination with half a mind to sightsee when he spies a ghost ship floating in the ocean!

With his new mace in hand, he and his allies fight off the wraiths, skeletons, and other varieties of undead monsters infesting the ship. And then, they finally come face-to-face with the enemy demon lord. But their opponent is a powerful dark magic user capable of launching attacks that inflict debuffs?! In order to defeat the enemy demon lord, Yuki will have to unleash his secret, explosive spirit magic!