Captain of the Harekaze. Belongs to the Navigation Department. Usually called "Captain" by the Harekaze class, but her childhood friend Moeka calls her "Mike-chan." She has a bright, positive personality and is an optimist who believes that "shipmates are family" and that "everything will work out" no matter the difficulty. She is afraid of lightning. She has incredible luck, such as winning the exact item she wanted from a lottery on the first try, never drawing anything but a "Great Blessing" at a shrine, and finding double yolks in eggs more than five times. She remembers the names of all 31 crew members plus 2 animals.

Deputy Captain of the Harekaze / Belongs to the Gunnery Department. Daughter of the prestigious Munetani family, which has produced Blue Mermaids for generations. The youngest of three sisters. She has a serious personality and is an honor student with no weak subjects. Her luck is remarkably bad, to the point where her catchphrase is muttering "I'm so unlucky." She dislikes the nickname "Shiro-chan" and prefers to be called "Deputy Captain" or "Munetani-san." While she maintains a serious and dignified attitude, she loves cute things and keeps a large number of stuffed animals in her room.

Gunnery Officer / Gunnery Committee. Belongs to the Gunnery Department. Nickname: Tama-chan. Reticent and poor at talking to people, she sometimes has awkward conversations and replies with "Ui." On the other hand, she is quick-witted and can perform instantaneous and accurate ballistic correction calculations, showing off the feat of intercepting and shooting down incoming shells from the Musashi with her own. She trusts Akeno, who understands her thoughts even with few words. She is close with Mei and they usually act together. She likes curry.

Torpedo Officer / Torpedo Committee. Belongs to the Gunnery Department. Nickname: Mei-chan. She wears a ribbon shaped like cat ears and a hoodie with a cat face design. Although small, she is strong-willed. She is close with Shima and they usually act together.

Record Keeper / Secretary. Belongs to the Logistics Department. Nickname: Koko-chan. She handles information gathering and recording the logbook. She has a gentle and polite manner but tends to escape from reality, having a delusion habit where she presents her own speculations and inferences in the form of a one-person play.

Chief Navigator / Navigation Committee. Belongs to the Navigation Department. Nickname: Rin-chan. In charge of steering. She has a poor sense of direction and is a coward. She tears up immediately when something happens but becomes lively when it's time to run away. Her family home is the Hinomisaki Offshore Maritime Shrine in Shimane Prefecture, and she helps out there as a shrine maiden.

Damage Control Officer / Beautification Committee Chair. Nickname: Hime-chan. She is skilled in engineering and builds portable shrines and food stalls herself for events. Her parents are from Kanda, Tokyo, and her blood boils with excitement whenever she hears about a festival.

Torpedo Crew / In charge of the No. 1 torpedo tube. Nickname: Jun-chan. She is good at ring toss. She frequently uses onomatopoeia like "Bang!" in conversation.

Torpedo Crew / In charge of the No. 2 torpedo tube. Nickname: Kayo-chan. She is good at bowling. Her grandfather was a sumo fan, and she is knowledgeable about sumo due to the influence of watching sumo programs on TV with him. Her favorite food is eggplant, and she is particularly fond of pickled water eggplant.

Captain of the Musashi. Nickname: Moka-chan. Akeno's childhood friend. She is an excellent student who entered as the top of the 121st class and became the captain of the Musashi.