In some ways, I feel like the "Sea Devil" (Ceratias holboelli), the deep sea anglerfish with the bioluminescent lure dangling from its forehead, is the perfect fish match for Kotone considering that the glowing lure is pretty analogous to dangling a 50-yen coin on a string to hypnotize people and also considering that the female Sea Devil, which is the gender you're picturing when we talk about the Sea Devil, attracts tiny males who permanently attach themselves to the female and eventually the combined organism becomes a genetic chimera, very analogous to Kotone's popularity at school except for the chimera part.
The downside of comparing the Sea Devil anglerfish to Kotone is that it's a very ugly fish and is also not one that they can really keep in normal aquariums due to how it can only survive at deep sea pressures.