Female. She rarely uses first-person pronouns, speaking in a slow, airy, and gentle manner. She is a creature (a monster or 'kaiai') antagonistic to Chiikawa and their friends, accompanied by two servants called 'Mermaids.' Among the monsters appearing in the Chiikawa series, she is notably rational; it is suggested that coexistence would have been possible if not for a 'certain reason.' As mentioned, due to this 'certain reason,' she began indiscriminately attacking and eating islanders. This led the islanders to issue a subjugation quest, drawing Chiikawa and other professional monster hunters to the island. However, Chiikawa and the others learn of the Siren's circumstances before hearing the full details of the quest, leading them to face the battle with conflicted hearts. She possesses a massive physique, ranking among the largest monster characters seen in the series to date. While her lower body is that of a typical fish-like mermaid, her upper body resembles a cat or a mammal (modeled after an 'inu-hariko' folk toy), and her hands are shaped like fish fins. Her appearance is unique, differing from both the common mermaid and the winged Sirens of Greek mythology, leaning closer to the mermaids of Japanese folklore. With her troubled eyebrows, large eyes, and cat-like mouth, many readers find her 'cute.' She is capable of speech and possesses high intelligence. Generally calm and composed, she is a rare monster capable of verbal communication. When she accidentally attacked Chiikawa and the others upon their first meeting, she apologized, showing she is not inherently evil. On the other hand, she is ruthless toward those she deems enemies, showing a fierce side that enjoys literally toying with the weak. She can be somewhat self-centered and selfish, often not listening seriously to others. Because of her immense power, she seems oblivious to how much her strength affects her surroundings. While rational, her fundamental sense of ethics differs slightly from human standards. She is a skilled singer, acting as the lead vocalist while the two Mermaids provide chorus support. She can manipulate plants with her singing voice, using it as a means of attack by extending nearby vines to capture enemies. Since her voice is amplified by the Mermaids' chorus, the plants' movements slow down if the Mermaids stop singing for any reason. The same happens if she moves too far away from the chorus. In terms of combat ability, she is exceptionally strong even among the monsters shown so far, easily defeating and capturing Rakko, the top-ranked hunter. (Though it's not definitive that she is stronger than Rakko, as he was trying to persuade her after hearing the circumstances, and got his leg caught in vines only after Momonga's attack was deflected toward him.) Her home ground is underwater, but her overwhelming power and plant manipulation make her a threat even on land. However, she seems sensitive to pain, reacting strongly to a small prick from a sasumata (man-catcher) and falling off a cliff in agony after a piece of candy was thrown at her uvula. She usually lives in a seaside cave with the Mermaids, but she can function in freshwater or on land, using her vines to move around quickly. Siren originally visited the 'Island' with three Mermaids for no particular reason. She took a liking to the heavily seasoned food offered (or sacrificed) by the islanders, who feared her as a supernatural being, and decided to settle there. Because her singing promoted crop growth, the island developed various local specialties and became a tourist destination. Thus, a relationship of 'co-prosperity' existed—though it was more of a slow invasion and domination based on mutual misunderstandings due to a lack of communication. One day, while playing in the sea with the Mermaids (using a squid as a ball), she accidentally collided with a boat carrying two 'Leaf' islanders she hadn't noticed. One of them, Futaba, was seriously injured (Siren remained unaware of their presence even after the collision). Later, while she was napping in her cave, one of the Mermaids was lured away with Shiruko Sand biscuits and captured by Hito-ha... Upon waking and realizing one Mermaid was missing, she found scales leading toward the islanders' village and concluded that 'the islanders caught and ate her.' She began indiscriminately attacking the islanders to find the culprit. 'I'll keep eating until someone confesses!' She declares that once she finds the culprit, she will put them in a 'perfectly sized cage' in a 'deep, dark place' to let them taste 'eternal life.' Her actions eventually lead to a total confrontation with Chiikawa and the others, exacerbated by the greedy Momonga's behavior. To counter the powerful Siren, Chiikawa and the others, with the help of Shima-Jiro, plot to feed her super-spicy curry to seal her singing voice. While the first bite was merely 'tasty-spicy' to her, she couldn't handle the curry reinforced with Carolina Reapers added by Shima-Jiro. Her face turned bright red, her pupils became swirls, and she writhed in agony. In the chaos, her tail struck Futaba, who had moved to protect Hachiware. Futaba was knocked unconscious. Seeing this, Chiikawa and the others pleaded through tears for her to stop attacking everyone. Siren screamed 'I get it!! I get it!!' and fled the scene at full speed in search of water.