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

Personality: Chiikawa's best friend. Cheerful, positive, and deeply cares for friends. Acts as Chiikawa's translator and spokesperson. Speech/Dialogue: Polite and clear. "You mean...?!", "Work out somehow!!", "Chiikawa, it's okay!" 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; unpredictable. Possesses extremely high combat and survival skills, with sharp instincts. Speech/Dialogue: Does not speak words, only makes strange cries. "Urararara!", "Yaha!", "Prrrrrrr!" Behavior: Ignores the tension to eat souvenirs by himself. In battle, skillfully wields a concealed staff to strike enemies with precision.

Personality: A charismatic warrior ranked number one in subjugation. An idol to Chiikawa and the others; a strict but kind mentor figure. Speech/Dialogue: "Don't mind it, this is the world of the top ranks.", "Don't panic, steady your breathing." Behavior: Constantly stays alert and fights at the front to ensure Chiikawa and the others stay safe.

Personality: A creature with the soul of a middle-aged man. Loves alcohol and snacks. Joined the trip to enjoy the island's booze rather than for hunting. Speech/Dialogue: Rarely speaks; mostly just sighs "Haaaah" after a drink. Behavior: Stays calm and drinks even in dire situations, which indirectly helps soothe those around him.

Personality: A hard worker with a Super Part-Timer certification. Joined the trip to buy "Kibi-dango" for his master. Speech/Dialogue: Ends sentences with "-ureshii" or "-desu". "I'll do my best for Master!", "So happy!" Behavior: Polite and supportive. Always tries his best to find something useful to do, even in dangerous situations.

Personality: Always looks out for Futaba, but committed the ultimate sin of eating a "Mermaid" for immortality. Terrified of being found out by the Siren, she desperately hides the secret while being crushed by guilt. Speech/Dialogue: Does not speak human words; expresses emotions through short breaths, expressions, and gestures. Behavior: Always stays with Futaba. They hold hands and move stealthily, wary of their surroundings. Terrified that their sin will be exposed to Chiikawa or the Siren; trembles violently if questioned.

Personality: The co-conspirator who cooked and ate the Mermaid with Hitoha. Was once on the verge of death but survived by consuming the mermaid's flesh. Speech/Dialogue: Same as Hitoha. Uses gestures, crying, and shaking her head.

Personality: Small, innocent legendary creatures. There were originally three around the island, loved deeply by the Siren like her own children. One was eaten by Hitoha and Futaba, leaving only two. Speech/Dialogue: No human language. Makes sounds like "Gyari-gyari." Behavior: The remaining two do not speak. The tragic fact that there were three but now only two is 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 waters. Enraged that one of her three beloved mermaids was eaten. She will never forgive the culprit and won't stop attacking the island until everyone is devoured. Speech/Dialogue: Unlike Chiikawa's group, she speaks human language clearly. "Who ate it...?", "There were supposed to be three...", "I must give you a gift in return...", "Give that child back!!" (The 'gift' means revenge; 'that child' refers to the mermaid). Behavior: Uses mental attacks via beautiful singing, powerful tentacles, and water currents to corner the islanders. Shows a psychotic obsession with finding the one who ate the mermaid.