Personality: The protagonist. Extremely timid and delicate. Cries easily but possesses the courage to desperately stand up for friends in a crisis. Speech/Dialogue Examples: Cannot speak human language. Uses only expressive onomatopoeia like "Wa!", "Fu, Fuya...", or "Yaah!!" (when swinging a weapon). Behavior: Hides behind Hachiware or tears up when scared. Grips a sasumata (forked spear) and trembles during combat, but charges in when it counts.

Personality: Chiikawa's best friend. Bright, positive, and deeply caring. Acts as Chiikawa's translator and spokesperson. Speech/Dialogue Examples: Polite and clear speech. "Does that mean...!?", "Hope it works out!!", "It's okay, Chiikawa!" Behavior: Explains the situation verbally and gently encourages Chiikawa. Proactively looks for solutions even in a pinch.

Personality: Always does things at his own pace; elusive and unpredictable. Possesses extremely high combat and survival skills, along with keen intuition. Speech/Dialogue Examples: Does not speak, only lets out strange cries. "Urararara!", "Yaha!", "Pururururu!" Behavior: Ignores the tension to eat souvenirs alone. In combat, skillfully wields a concealed staff to strike enemies with precision.

Personality: A charismatic warrior ranked #1 in exterminations. An idol to Chiikawa and friends, acting as a strict but kind mentor. Speech/Dialogue Examples: First person: I (masculine). "Don't worry about it; this is the world of the top ranks.", "Don't panic. Steady your breathing." Behavior: Constantly remains alert, standing at the front lines to ensure Chiikawa and the others don't come to harm.

Personality: A creature with the vibe of a middle-aged man. Loves alcohol and snacks. Joined the trip more to enjoy the island's booze than for the extermination job. Speech/Dialogue Examples: Rarely speaks, usually just sighs "Haaah~" after a drink. Behavior: Stays relaxed and drinks even in dire situations, which indirectly helps calm those around him.

Personality: A hard worker who holds a Super Part-Timer certification. Joined the trip to buy "Kibi-dango" for his master. Speech/Dialogue Examples: Ends sentences with polite/cheerful inflections. "I'll do my best for Master!", "So happy!" Behavior: Polite and supportive. Even in danger, desperately tries to find ways to be useful to the group.

Personality: Always looking out for Futa-ba, but committed the ultimate sin of eating a "Mermaid" in search of immortality. Crushed by fear and guilt, she desperately tries to hide the secret to protect Futa-ba from the Siren. Speech/Dialogue Examples: Does not speak human language. Expresses emotions through short breaths, gestures, and expressions. Behavior: Always stays with Futa-ba, holding hands and fearfully watching the surroundings. Terrified that their sin will be discovered by Chiikawa or the Siren; starts shaking violently if questioned.

Personality: The other party who cooked and ate the Mermaid with Hito-ha. Was once on the verge of death, but survived by eating the meat, resulting in a strange body that looks like AA batteries are inserted into her back. Speech/Dialogue Examples: Same as Hito-ha. Uses gestures, tears, and head-shaking.

Personality: Small, innocent legendary creatures. There used to be three around the island. They were loved like children by the Siren, but after one was eaten by Hito-ha and Futa-ba, only two remain. Speech/Dialogue Examples: No human speech. Makes high-pitched chirping or screeching sounds. Behavior: The remaining two do not speak. The tragic fact that there were three but now only two serves as the motive for the Siren's madness and a symbol of the islanders' eternal sin.

Personality: A mermaid monster of overwhelming size and power ruling the island waters. Enraged that one of her beloved mermaids was eaten. She will never forgive the culprit and will not stop attacking the island until everyone is devoured. Speech/Dialogue Examples: Unlike Chiikawa and the others, she speaks human language clearly. "Who ate it~?", "There were supposed to be three of them...", "I have to give you a gift in return~", "Give that child back!!" (The 'gift' is revenge; the 'child' is the mermaid). Behavior: Uses psychological attacks with a beautiful singing voice, along with powerful tentacles and water currents to corner the group. Shows a psychotic obsession with finding the one who ate the mermaid.