A girl themed after the ancient fish, the coelacanth. She has deep blue hair, hair ornaments reminiscent of fish fins, and thick, fleshy fins on her back and arms characteristic of a coelacanth. She is an excellent swimmer and possesses vast knowledge of ancient life and marine ecology. Her personality is quiet and composed, yet she is kind and deeply cares for her friends. While she usually speaks slowly, she becomes suddenly talkative when the subject turns to the ocean or ancient organisms. Her legs and feet are shaped entirely like those of a human girl, not like fish fins. Likes: Fish dishes, seaweed salad, ramune soda.

A girl themed after the ancient organism, the horseshoe crab. She has reddish-brown hair, hair ornaments resembling a carapace, a hard shell on her back, and a long telson (tail spine) at her waist. Despite her small stature, she possesses immense stamina and defensive power, specializing in protecting her allies with a large shield. She is cheerful, active, and loves taking care of others—a big-sister figure to everyone. While usually full of energy, she shows a strong sense of responsibility when it comes to protecting her friends. Her legs and feet are shaped entirely like those of a human girl, not like the legs of a horseshoe crab. Likes: Fried shrimp, crab cream croquettes, takoyaki.

A girl themed after the ancient organism, the nautilus. She has silver-white hair, hair ornaments featuring the nautilus's spiral pattern, and a beautiful spiral shell on her back. She excels at underwater activities and is highly knowledgeable about ancient life and marine environments. Her personality is easygoing, gentle, and intellectual. She is a bit airheaded and tends to lose track of her surroundings when immersed in research. She spends much of her time in the library or laboratory but is surprisingly fond of adventure. Her legs and feet are shaped entirely like those of a human girl, not like the tentacles of a mollusk. Likes: Seafood pasta, clam soup, milk tea.

A girl themed after the ancient fish, the lungfish. She has pale green hair, fin-like hair ornaments, and soft fins on her back and arms characteristic of a lungfish. Uniquely, she can function on land as well as in water, making her an expert in fieldwork involving rivers and wetlands. Her personality is calm and kind, with a slightly relaxed pace. She is the type to naturally help anyone in trouble; though usually laid-back, she shows great initiative when the situation calls for it. Her legs and feet are shaped entirely like those of a human girl, not like fish fins. Likes: Cucumbers, river fish dishes, melon soda.

A girl themed after the ancient reptile, the tuatara. She has deep green hair, a row of small spiky scales on her back, and the characteristic markings of a tuatara on her head. She excels at observations in forests and rocky areas and is well-suited for nighttime fieldwork. Her personality is taciturn, calm, and a bit independent. While she is socially reserved, she watches over her friends closely and offers subtle help when they are in need. She becomes unexpectedly passionate when observing ancient life. Her legs and feet are shaped entirely like those of a human girl, not like the hind legs of a reptile. Likes: Tree nuts, grilled fish, matcha ice cream.

A girl themed after the sturgeon, a lineage of fish dating back to ancient times. She has silver-gray hair, hair ornaments resembling the hard scutes of a sturgeon, and distinct scute patterns on her back and shoulders. She is skilled at surveys in rivers and lakes and is knowledgeable about ancient and aquatic life. Her personality is gentle and refined, yet she possesses a strong core and a sense of responsibility. Usually calm and quiet, she displays surprising decisiveness when protecting her friends. She also has a side that enjoys talking happily about fish and waterfronts. Her legs and feet are shaped entirely like those of a human girl, not like a fish tail or fins. Likes: Salmon rice balls, river fish dishes, white peach soda.

A female teacher themed after the giant salamander, which has lived since ancient times. She has deep brown hair and dark brown markings characteristic of a giant salamander. She teaches paleontology, biology, and waterfront fieldwork. Her personality is as relaxed and easygoing as a capybara. She always has a soft, sleepy aura and speaks at a slow pace. Even if students play pranks or make mistakes, she generally forgives them with a smile and a "there, there." However, she is strict regarding the mistreatment of life, senseless harming of creatures, or life-threateningly dangerous behavior. In those moments, she puffs out her cheeks slightly and stares them down with lowered eyebrows in a cute way. It isn't a scary face, but it carries a strange, adorable pressure. Her body, legs, and feet are shaped entirely like those of a human woman, not like the legs of an amphibian. Likes: Wild vegetable dishes, salt-grilled river fish, warm hojicha tea.