Some residents of a small village hear a crash, and head to the chapel to find a hole in the roof and a black-winged baby resting on the altar.
Eleven years later, a man approaches the ringmaster of a circus, hoping to sell what he claims is a fish. The ringmaster checks inside a large sealed container and is shocked to find a child submerged in water. The seller assures the ringmaster that the child is not dead, and then the child turns to face the ringmaster.
Some time later, the circus put on a performance, and guests enter the main tent. The ringmaster presents the "Mermaid Princess" to the crowd, warning them not to stare for long or be caught under the mermaid's spell. The mermaid notices a boy with his head poking through a hole in the tent. The ringmaster follows the mermaid's gaze and sees the boy who tries to escape but finds himself stuck. One of the circus employees pulls him into the tent, but he sprouts black-feathered wings, tries to fly away and pulls the tent down in the process. The boy crawls from the tent, but is knocked out by the mermaid, a boy called Husky, using a rake.
That night, the ringmaster is looking over the boy, disappointed that the wings aren't white since he could have presented him as an angel in the circus. Husky enters the room and questions whether the boy is a +Anima; the ringmaster confirms this and shows Husky the boy's mark on his shoulder. The ringmaster divulges his plan to use the boy in the circus, and Husky gets annoyed by the ringmaster's greed. He compliments Husky on how successful he has helped make the circus, but Husky complains about the cheap pearls they use as props in the mermaid act; he promises to get Husky some better ones. Husky wants money as well as the pearls, but the ringmaster is unwilling, and claims to own Husky who argues that slavery is illegal, so he will leave the circus if not paid. The ringmaster accuses Husky of plotting to leave regardless, having found another +Anima. He holds out a locket, which Husky tries to grab. The ringmaster uses the locket as leverage to keep Husky in line, and then leaves the room.
The winged boy, Cooro, rolls over and introduces himself to Husky; he invites Husky to leave with him. Husky is confused by the sudden offer, but is even more confused to find that Cooro's reasoning is that Husky can catch fish for him to eat. Cooro explains that he is searching for other +Anima, and thinks it will be fun to travel together. Husky is annoyed by the offer; he leaves the room, slamming the door behind him, but immediately comes back just to explain that he only dresses up as a girl for the money, and the slams the door again on his way out. Cooro had no idea of Husky's sex. Husky is angry that Cooro was in complete control of the negotiation, despite him being the captor; he resolves to leave the circus by himself.
The ringmaster is in bed, snoring. Husky sneaks into his room, takes a pouch from beneath the pillow, and then reaches for the locket around the ringmaster's neck. He wakes up and grabs Husky's wrist, and two of the circus employees step out behind Husky. They tie Husky up, submerged in the mermaid water tank.
The next day, the ringmaster explains to Cooro that to pay his debt for watching the performance, he is going to have to work for him. He guides Cooro into the tent where Husky is trapped. The ringmaster explains that it is part of the show, and Cooro must act like he has captured Husky. They let the customers into the tent. Husky tries to convey to Cooro that it isn't an act, but can't say anything since he is underwater.
When the performance begins, Cooro starts crying and loudly complains to the ringmaster that Husky shouldn't be tied up. The crowd sympathize with the children, and while the ringmaster is distracted trying to calm the situation, Cooro steals the locket. He then sprouts his wings, flies up, and tips the water tank to free Husky, knocking down the tent again in the process. Cooro questions why the locket is so important, but Husky demands he be untied first. The ringmaster and his employees surround the children, Cooro lifts Husky into the air and flies away.
Husky enjoys the feeling of flying, but it doesn't last long as they fall into a lake. Husky drags Cooro up onto a water lily. Cooro had never flown carrying something so heavy, and he was also hungry, so unable to fly any further. Cooro hands the locket to Husky, who opens it and removes two earrings and places them on his ears. Cooro compliments the earrings, and Husky blushes and turns away. Cooro's stomach grumbles, and Husky concedes to catching him some fish on the condition that they never fly again.