In the Land of Leadale, Vol. 3 (light novel)

Now a full-fledged adventurer, the high elf Cayna is back on the road to find the next Guardian Tower. She stops at a fishing village where there’s talk of a castle at the bottom of the ocean, but she finds the village covered in a strange mist and overrun with scores of undead! After a chance reunion with one of her former guild members, Cayna has another boss battle awaiting her…and it involves a pirate capain and an eerie ghost ship!