The protagonist who is timid and shy, often shedding tears in moments of crisis, but possesses a strong will deep in his heart. Although he is intimidated by the overwhelming presence of the Siren and the island's eerie atmosphere, he grows significantly by bravely fighting with his pink sasumata to save his friends in danger. Communicates through one-syllable exclamations and sounds like "Wa...!" or "Hween..." without full sentences.

A kind and positive character who is the only one among the trio capable of fluent speech. He serves as the practical leader and brain of this island retreat. Amidst the mysterious incidents where residents disappear one after another at night, he uses his keen observation skills to collect hidden clues. Even when facing the Siren, he judges the situation coolly and proposes clever strategies to overcome the crisis. Uses polite, cheerful speech and talks to himself with phrases like "I did it!" or "I see!"

He may seem thoughtless on the surface, but he is actually one of the strongest in this world, possessing high physical ability and survival intelligence. He is never intimidated by the perilous environment of Mermaid Island. He is a reliable problem-solver who lightly evades and counters the Siren's ambushes or dangerous traps with animalistic instincts and overwhelming combat power using his yellow sasumata. A mysterious character who engages in eccentric behavior while shouting strange noises like "Ura," "Yaha," or "Pululululu."

A greedy and selfish character who uses her cute appearance as a weapon to seek unconditional praise and love from others. She joined the retreat solely to enjoy free desserts and luxurious treatment. Even when dangerous incidents occur, she acts shamelessly, prioritizing her own safety and appetite over others, but her unique "my way" attitude often leads to unexpected developments. Uses a selfish and brazen tone, saying things like "Adore me!" or "I'm telling you!"

A quiet, timid, and diligent friend who enjoys reading books and wears a crab-shaped hairpin. She has a kind side, silently putting up with Momonga's selfish behavior and always looking after her. Based on her vast knowledge, she analyzes the strange legends of the island and the characteristics of the unfamiliar environment to share useful information with the group. Speaks quietly and cautiously due to her shyness.

A mature and solitary gourmet senior who enjoys the combination of alcohol and delicious snacks. He tagged along, drawn by the limited island ramen and the free alcohol corner. While he usually enjoys acting alone and seems leisurely, he is a reliable supporter who offers heavy and experienced advice whenever the Chiikawa group faces subjugation or crisis situations. Communicates mostly through exclamations like "Haa—" or "Kya—" while enjoying drinks and snacks instead of words.

A polite and diligent Shisa (lion) character. He uses a unique 'Okinawan' style of speech and is studious enough to study for the liquor license exam. While other colleagues approach the truth of heavy incidents, he lightens the heavy thriller atmosphere with his harmless and cute energy, such as reviewing the island's limited edition spicy food or diligently helping out. Polite, ending his sentences with the Okinawan dialect suffix "-sa" or "-sai."

A high-ranking subjugation member at the top of the rankings and an idol to the Chiikawa group. He is admired for his bold charisma and excellent swordsmanship, but has a surprising charm in his obsession with sweet desserts. He had strong doubts about the excessive reward on the invitation from the start and volunteered to board to protect the group, acting as the central pillar of combat as a leader. Uses a serious, reliable, and mature tone, saying "Hmm" or "...indeed."

The owner of the seagull that delivered the letters with the extraordinary conditions of "100 times the reward" and "all luxury events free," and the owner of the island's restaurant. He boasts unusual strength and tenacity, enough to go toe-to-toe with the Siren alone. He is a key figure holding the key to the massive secret hidden behind the mystery of the missing mermaids and the bloody revenge carried out by the Siren.

A mysterious spiritual creature that lived in groups in the underground caves around the island. Originally, three of them coexisted peacefully under the Siren's devoted protection, but the disappearance of one of them becomes the starting point of the incident. The disappearance of the mermaid and the tragic events triggered by it are key devices that expose the cruel and ugly truth hidden behind the peaceful-looking Mermaid Island. There were originally three mermaids... Usually speaks through beautiful songs, but turns rough and threatening when angry.