The protagonist who is timid but finds courage for his precious friends. He is a bystander and observer who witnesses the most brutal truth in this episode. Despite knowing the truth, he suffers a great mental shock, experiencing a bitter moral dilemma where he must choose silence because he cannot change anything. He cannot speak and expresses himself through actions and facial expressions.

Chiikawa's positive best friend who can speak. He struggles to protect his friends during the island's crisis and serves as a spiritual pillar, taking risks to propose plans to save comrades captured by the Siren.

• Usagi: The one who first found the flyer for the island with the extraordinary pay and led the Chiikawa group to the island. As always, he engages in bizarre behavior, but at every critical moment, he saves the team with his unique survival instincts and combat power.

Cute-looking island residents with tangerines on their heads.

Kurimanju: Joins the trip to the island to enjoy drinks and snacks as usual, leisurely enjoying the island's limited edition food.

Momonga: A selfish character obsessed with cuteness who followed the group to the island to eat delicious food for free. While not helpful in battle, he plays an unexpected scene-stealer role with his characteristically selfish behavior.

Rakko: The strongest exterminator in the Chiikawa universe. Seeing the flyer Usagi brought, he senses something suspicious, noting that "the pay is too high," and accompanies the Chiikawa group to protect them. He serves as a reliable shield, fighting back with powerful swordsmanship in direct combat with the Siren.

• Appearance: An uncle-like character with a large leaf on his head and a sturdy, robust build. • Personality: He looks blunt but is deeply affectionate and very kind. He has a warm heart, sincerely worrying about and taking care of the Chiikawa trio who are nervous and scared on the unfamiliar island.

Siren: A powerful and giant god-like being who rules the seas of Mermaid Island. Originally of a gentle nature, she goes insane with rage upon learning that a fellow mermaid was murdered and eaten by island residents.

Mermaids: Legendary creatures that act with the Siren. There were originally three, but one was caught and eaten by Hitoha, so only two remain. They assist the Siren's ability to control plants by providing harmony when she sings.