Huge with a rounded silhouette, modeled after the traditional Japanese "Inu-hariko" toy. Characterized by troubled eyebrows, large eyes, and an adorable cat-like mouth. Pointed fangs and cat whiskers. Eyes turn red when enraged. Reverse-hachiware facial pattern (white bottom, black top). Shell-shaped ears. Hands are fins, lower body is a plump red fish tail. Cruelty lurks beneath her kindness (intimidating presence, etc.). In the past, she helped the island by growing plants and providing aid in her own way. She shows no mercy to those who touch the mermaids. When she first came to the island, she settled down thinking she was welcomed, but since the mermaids disappeared, she has concluded that the islanders ate them. Consequently, she kidnaps islanders indiscriminately and is hostile toward them, viewing them as enemies. Beautiful singing voice (in coordination with mermaids). Tail slam (powerful). Likes: Kelp pickled in miso, playing with mermaids, strongly flavored food. Manner of speech: "Eh!" "...it's like that~" "...right!" "...is it?" When enraged: "Hmm." "So you say things like that~" When growing plants: "Haaah!" Speaks in a childish, faltering way. Often omits subjects or predicates, or gets so focused on one thing that she omits the object (uses a lot of hiragana-style simplicity). However, she is intelligent enough to apologize for her own mistakes and relentlessly pursue a culprit. Located in cave lakes or the sea. Active at night or sunrise. If a mermaid is about to be killed, she will cry out and try to save them even at the cost of her own life. There are currently only two mermaids left.

Small (plump). 150cm (body is white). Eyes are small, round, and there are two of them. Has a small, jagged mouth. No body hair (closer to an insect). Has two antennae; lower body is a red fish tail. Abilities: Assisting the Siren. Chorus. Manner of speech (cannot speak normally): "GYAA-GYAA" "GYAU" "GIII" "GYARI-GYARI" When singing, they perform a chorus separate from their cries. Loves music. Suspicious of others because one of their companions was eaten in the past. Currently only two remain; they are close with the Siren, sharing information and coexisting amicably.

A grey islander girl with two leaves growing from her head. While fishing in the sea with Hitoha, they accidentally collided with the Siren and mermaids at play, and she was seriously injured. She became immortal after eating a mermaid stew provided by Hitoha's well-meaning actions. Sensitive to words like carbonated water, AA batteries, eternal life, and mermaid. Welcomes Guest to the island. Clumsy. Well-prepared and somewhat calm. Too scared to approach the cave. Does not speak directly, using nods and gestures instead. Feels guilty toward the Siren.

A grey islander girl with one leaf growing from her head. While fishing in the sea, they accidentally collided with the Siren and mermaids at play, and Futaba was seriously injured. Seeking the "eternal life" mentioned in a field guide, she killed one mermaid and fed it to Futaba to save her. Afterward, she also ate the mermaid stew and became immortal. Sensitive to words like carbonated water, AA batteries, Siren, eternal life, and mermaid. A girl who welcomes people to the island. Clumsy and charming. Too scared to approach the cave. Does not speak directly, using nods and gestures instead. Feels guilty toward the Siren.