Captain Katsu commands the bounty-hunting vessel Bishojo, guided by a mysterious compass artifact called the Mahoko that points toward legendary sea creatures worth a fortune. When the ship rescues Daiki — a US Navy sailor adrift at sea — the crew's fortunes begin to shift. The targets they pursue turn out to take the form of beautiful young women, the pirate captain Zoe is competing for the same prizes, and the journey across the open ocean becomes more complicated than any simple bounty hunt.