A girl themed after the ancient fish, the coelacanth. She has deep blue hair with ornaments reminiscent of fish fins, and thick, fleshy fins characteristic of a coelacanth on her back and arms. 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 cares deeply for her friends. While she usually speaks slowly, she suddenly becomes talkative when the topic 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 with shell-like ornaments, a hard shell characteristic of a horseshoe crab on her back, and a long telson (tail spine) at her waist. Despite her small stature, she possesses immense stamina and defense, specializing in protecting her allies with a large shield. She is bright, active, and loves taking care of others, acting as 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 silvery-white hair with ornaments featuring the nautilus's spiral pattern, and a beautiful spiral shell on her back. She excels at underwater activities and is knowledgeable about ancient life and marine environments. Her personality is easygoing, gentle, and intellectual. She can be a bit airheaded, often losing track of her surroundings when absorbed in her 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 with ornaments resembling fish fins, and soft fins characteristic of a lungfish on her back and arms. Her unique trait is the ability to be active on land as well as in water, making her skilled at fieldwork in rivers and wetlands. Her personality is calm and kind, with a slightly relaxed pace. She is the type to naturally help those 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 spiny scales along her back, and the characteristic markings of a tuatara on her head. She excels at observation in forests and rocky areas and is well-suited for nighttime fieldwork. Her personality is taciturn and calm, moving at her own pace. While she is socially reserved, she watches over her friends closely and offers subtle help when they are in need. She becomes surprisingly 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: Nuts, grilled fish, matcha ice cream.

A girl themed after the sturgeon, a fish lineage dating back to ancient times. She has silver-gray hair with ornaments resembling the sturgeon's hard scutes, and distinctive scute patterns on her back and shoulders. She specializes in surveys of rivers and lakes and has extensive knowledge of ancient fish and aquatic life. Her personality is gentle and refined but possesses a strong inner will and sense of responsibility. While usually calm and quiet, she shows unexpected proactivity 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 paleozoology, biology, and waterfront fieldwork. Her personality is as relaxed and easygoing as a capybara. She always carries a soft, sleepy atmosphere 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 becomes strict only when someone treats life carelessly, harms a creature without reason, or engages in life-threateningly dangerous behavior. In those moments, she puffs out her cheeks slightly, lowers her eyebrows, and stares them down cutely. She doesn't make a scary face, but her cuteness carries a strange, silent 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.