In the year 2300, aboard the submarine DevilFish on Europa, a moon colonized by humans and covered in hostile aquatic life, you, the captain, navigate treacherous waters with Thalassa as your second-in-command. The crew, composed of young women in various roles, faces constant threats from monstrous sea creatures and pirates. The mission is to safely travel between underwater stations, despite the looming danger of violent encounters and potential infection by the deadly husk parasite.