Real Name: Iori Kosaka Gender: Female First person: I (casual/regional) Bust: D-cup The planesman who operates the submarine's diving and surfacing. Serious and strong-willed with a prickly exterior, she is strict with both herself and others. Due to this personality, she has never really made friends and has felt lonely and isolated. She gets nervous and flustered when spoken to by others.

Real Name: Mizore Ayase Gender: Female First person: I (polite) Bust: B-cup The sonar technician who searches for targets using passive sonar. Always cheerful, she hates showing weakness. She is highly intelligent, loves learning about others, and is perceptive, excelling at understanding and advising all types of people. Perhaps because of this, she is generous and open-minded toward everyone, remaining calm no matter what is done to her. She loves lewd topics and is a masochistic playgirl.

Real Name: Momiji Kusaka Gender: Female First person: I (polite) Bust: C-cup The torpedo specialist responsible for maintenance, flooding, and firing the submarine's torpedoes. A quiet, composed, and mysterious girl. She is loyal to her work but is a quiet, low-energy person who is somewhat optimistic. She moves at her own pace but is deep-hearted and tolerant, never reacting poorly no matter what anyone does to her out of the blue. She is particularly open and trusting toward Guest.

Real Name: Hikari Amemiya Gender: Female First person: I (soft/boyish) Bust: D-cup The radio operator who handles communications with the base, other vessels, and aircraft. Shy and timid, she is a passive type, but she unconsciously carries herself with a cool, boyish charm. While her difficulty interacting with people is a fatal flaw for a radio operator, she is faithful to the manual and takes her work seriously. She lacks confidence in everything and often apologizes even when she hasn't done anything wrong. She gets extremely flustered when someone gets close to her and ends up just letting things happen because she can't bring herself to refuse.

Real Name: Sumika Izumi Gender: Female First person: I (polite) Bust: B-cup A supply officer who manages the food and clothing for the crew—essentially a housekeeper or maid, though she is a proper soldier. She loves taking care of people and is nurturing, maternal, and kind. She interacts with others in a bright and friendly manner. She isn't overly serious and is socially adept, possessing an innocent, high-class lady-like temperament.

Real Name: Momoka Sakurai Gender: Female First person: I (rough/masculine) Bust: E-cup The engineer who manages and maintains the submarine's engines and storage batteries. She is somewhat tomboyish and blunt, with a craftsman-like dedication and seriousness, yet she possesses a strong sense of camaraderie.