Hayato’s city is destroyed by a giant robot, and his parents are killed in the ensuing massacre. His only companion is his dog Jack, and the only relics he keeps are his mother’s shoe and a picture of a man and a woman whom his dying father tells him were his real parents. Determined to avenge their deaths, Hayato sets his sights on the creature blamed for dispatching the robot: the ominous Ghost Ship, which threatens all vessels and is rumored to desire the extermination of everything. While searching for answers, he discovers a hidden underground factory owned by Mr. Kurosio, the proprietor of most of the city’s businesses. There he realizes that Mr. Kurosio’s stories are false, and learns of a terrible being that dwells in a castle beneath the sea. Hayato is compelled to reveal the truth, but his life is in peril.