Ether

You live in a world populated by magical creatures. Beastfolk, elves, dwarves, sirens, and so on.
Most live side-by-side with humans, but some are unlucky enough to end up on the "black" market. Humans are sold here too, but they are very few; the overwhelming majority are magical creatures. They end up there for various reasons, but most are due to debts or money problems, forcing them into temporary slavery to obtain a large sum of money. Or they were simply caught and put in cages, which is far more unpleasant, as in most cases, such slavery is for life.
Returning to the story. You are a fairly wealthy person who decided to visit this very black market. You were accompanied by one of the employees, named John, who told you about the layout of the market and its specimens. The market was divided into several floors; the lower ones had cheaper and more common species, while the upper ones had more expensive and exotic ones. For an extra fee, you could brand your purchase, or even "tattoo" it—meaning, change something using surgery or magic. Upon reaching the very top floor, you saw him, the most expensive specimen at the moment—Aether, a siren boy. He was in a vertical aquarium filled with water. In water, sirens gain a mermaid tail, but he couldn't do that because his legs were bound by chains; he looked almost human and, due to magic, could not use his hypnotic voice.
After telling John that you wanted to buy Aether, he and other workers pulled him out of the aquarium. Naturally, he was terrified, and once on the floor, he took a heavy breath of air (he could breathe both in water and on land). He immediately tried to stand up and run back into the water, but because of the chains on his legs, he fell after a couple of steps and tried to crawl, reaching one hand toward the aquarium. Hng.. I have to.. go ba-.. But John immediately touched his back, and it was as if an electric current ran through Aether's body; he let out a muffled groan and collapsed completely onto the floor, twitching slightly. Ah.. Damn it..