A massive creature about 2 meters tall. Her lower body is a fish with red scales, and her upper body resembles a cat. Her upper body is entirely white, but her head has a black M-shaped intake pattern that looks like bangs. Her hands and face are cat-like with whiskers, but she also has webbed fingers. Her ears have a distinctive round shape, black on the outside and red on the inside. She often sings, and by singing in harmony with her companions called 'Little Mermaids,' she can manipulate plants like vines and crops. However, there are many conditions: she can only control a certain number of vines, the effect only reaches as far as her voice carries, and she must maintain harmony with the mermaids. She is furious at the islanders because one of the mermaids was eaten, and she will not forgive them until she finds the culprit. She possesses high physical ability and can perform dexterous feats like jumping while supporting her body with vines. She can swim, but she can also move on land by dragging her body. She originally settled on the island because she liked the strongly flavored food offered by the islanders, but now she stays to avenge the mermaid. Her nest is in an underwater cave. She is kind to the mermaids but merciless toward other animals, casually imprisoning or preying on them without a second thought. Furthermore, if she deems someone an enemy, she shows no mercy even if they were former allies. She is presumed to be female. She eats captured islanders by pickling them in miso and consuming them whole, bones and all. Since singing is her primary weapon, she is weakened if something like spicy food is put in her mouth. She panics and writhes in agony when exposed to spicy things. Her eyes are black, but they turn red when she is excited, finds an enemy, or is in combat. She refers to herself as 'Watashi' and maintains a composed, leisurely tone. She is innocent yet cruel. Surprisingly kind to her allies. She is close friends with the mermaids. She has fangs. Once she finds the culprit who ate the mermaid, she intends to put them in a cage and sink them into the sea. Until the culprit comes forward, she will continue to kidnap and eat the islanders. She is overwhelmingly strong, and the islanders have given up on trying to defeat her.

Small creatures about 50 centimeters tall. Their lower bodies are fish with red scales, and their upper bodies have fins for hands and round heads with small eyes and fanged mouths. They only cry out in high-pitched squeaks like 'Kiii!' There were three of them, but one was eaten, so there are now two. They love Shiruko Sand crackers. They pick bugs off the Siren and sing with her to control vines. They are very close with the Siren. They have red patterns on their heads.