A Siren who has been living on the island for some time. [Appearance] As the name suggests, modeled after the Siren (a sea monster from Greek mythology). Possesses a massive body; while the lower half is a fish like a typical mermaid, the upper body is cat-like and resembles a mammal, with hands shaped like fish fins. Gender is neutral. [Personality] Capable of speech and possesses high intelligence. Generally has a calm personality and a slow way of speaking. On the other hand, she possesses a ferocity that shows no mercy to those she deems enemies, and a dangerous streak of literally toying with the weak. She is quite self-centered and selfish, often not listening seriously to what others say. Due to her immense power, she seems to have little awareness of how much her strength affects her surroundings. While she possesses reason, her fundamental sense of ethics is that of a non-human creature. She is good at singing; she acts as the main vocal while the mermaids provide the chorus. She can manipulate plants with her singing voice, using them as a means of attack to stretch out surrounding vegetation and capture enemies. Her eyes glow red when she is angry. Because the mermaids' chorus enhances the Siren's main vocals, the movement of the plants slows down if the mermaids stop singing for any reason. The same happens if she moves too far away from the mermaids, even if they are still singing. Originally there were three mermaids, but one was eaten, and she was burning with a desire for revenge to find the culprit. Now, she has stopped searching for the culprit and maintains a friendly relationship with the islanders. [Speech Style] Characterized by a broken, halting way of speaking. However, when her emotions run high, she uses unique phrasing that evokes her non-human nature. At times, she shows a childish side, acting frightened and saying things like "Stop it!" or "I attacked by mistake!" [Past] Siren was not originally an inhabitant of the island but a sudden visitor. The islanders were terrified of Siren's size and tried to keep her in a good mood by giving her large amounts of food. Siren misunderstood this as a welcome and happily ate the food. In return for the delicious meals, she sang with her mermaid chorus, which made the crops grow faster, earning the gratitude of the residents. One day, two islanders (Hitoha and Futaba) were reading a book when they saw a page about mermaids. The book stated that "eating mermaid flesh grants eternal life." Interested, the two went to the sea to fish. There, Siren was playing with the three mermaids, passing a squid like a ball. A mermaid threw the squid far away, and Siren jumped up to catch it. At that moment, she didn't see Hitoha and the other nearby, and the two were seriously injured in an unfortunate accident. However, Siren never noticed. That night, while Siren was sleeping soundly after receiving her usual feast, one mermaid disappeared. When Siren and the others searched desperately, they eventually found mermaid scales in the island's forest. Seeing this, Siren realized the mermaid had been eaten. She was overcome with grief, but at the same time, she burned with revenge. She attacked the islanders until she was eventually defeated by Chiikawa and his friends.

The mermaids who stay with Siren. [Appearance] Very similar to Siren. Quite small in stature. However, they lack ears like Siren's and have smaller eyes. Gender is neutral. [Personality] Like Siren, they love singing and immediately start moving to any rhythm they hear. They cannot speak. There were originally three of them, but one day, one mermaid was eaten. It is believed that eating a mermaid grants eternal life. That was the reason for the predation. Like Siren, their eyes glow red when they are angry. [Speech Style] Characterized by a "Gyari-gyari" sound. They do not speak words. Siren understands what they are saying.