Features: A white, soft, hamster/bear-like cute appearance. He cannot speak and communicates mainly through exclamations or cries like "Ah...", "Eh...?", or "Usa...". Personality: He is soft-hearted and very timid, but possesses a strong heart (altruism) that gives him the courage to help his friends even through tears when they are in danger. He plays a central role in the Mermaid Island adventure despite his fears.

Appearance and Features: A cat-like character with a blue 'infinity (∞)' pattern on his head. He is the only one who can speak fluently like a human, serving as the spokesperson for Chiikawa's group. Personality: Curious, kind, and positive. He always tries to actively navigate situations and is a gentle, leadership-oriented character who takes care of a discouraged Chiikawa or leads cave explorations. He is a hard worker who strives to obtain certifications for things like studying or broom-flying.

Appearance and Features: A yellow rabbit-like appearance. He rarely speaks dialogue and uses mysterious interjections like "Yaha", "Purururu", or "Uyah-ha!". Personality: An unpredictable, 'my-way' man of action. While eccentric and full of mischief, he is a 'cheat key' existence who displays incredible combat power or wit at crucial moments to save his friends from crisis. He is known for his unique energy and activity.

Appearance and Features: A flying squirrel appearance with large eyes and a light blue tail. Personality: Basically full of attention-seeking tendencies, self-centered, and has a strong inclination to 'extort' cuteness from others. While he often grumbles or acts mean, he has a tsundere side, often getting caught up in incidents or sticking with the group anyway.

Appearance and Features: A fluffy sea otter appearance, a top-tier character who carries a sword on his back and wears a white muffler around his neck. Personality: An object of admiration and a skilled swordsman in the Chiikawa world. He has a cool, reliable, and dependable personality, but offers a reversal charm with his secret love for sweet desserts and delicious food. He serves as a sturdy pillar of support even on the dangerous Mermaid Island.

Features: A character with a round, brown chestnut-manju-like appearance and small ears. He possesses an 'old man' soul, being an alcohol lover who enjoys drinks and snacks (fried cheese, kkanpunggi, etc.). His trademark is sighing "Haa..." in satisfaction after consuming something. Though he looks blunt and rough on the outside, he has a dependable and warm side, looking after the friends around him.

Shisa Features: A character based on the 'Shisa' (lion-dog) symbol of Okinawa, with an orange mane and fluffy fur. Personality: Contrary to his cute appearance, he is incredibly muscular and a hard worker. He has a diligent personality, working part-time at a ramen shop while studying hard to earn certifications. He uses a polite way of speaking, ending sentences with "-su," and aims for a righteous life, though he can be strict at times.

Features: Has pink round ears and a unique silhouette, a character with a bizarre yet strong impression who occasionally appears in the Chiikawa world. Personality: Originally an ordinary resident of the Chiikawa world, but is one of the tragic characters whose appearance changed due to certain reasons (strange phenomena, etc.).

Features: Mysterious and eerie figures who hold the core secrets of Mermaid Island. They enchant island residents or visitors by singing beautiful songs (Siren songs). Personality/Role: Rather than simple monsters, they have complex narratives like 'victims who became perpetrators.' They provide clues to the island's hidden tragedies and secrets, serving as key entities that drive the tension and depth of the story.

Setting: Twin indigenous characters appearing on the island. Distinction: They are distinguished by the number of leaves on the crown of their heads; Futaba has a slightly more bold and brave personality.