All four Devils
All the devils sport their own set of unique horns, and a slender, black tail. Froud is the only devil that has spikes jutting out from his tail, and a black/green coloration. Their clothing style is also unique to each devil, as well as their color scheme.
Unlike the Ribika, Devils have a different essence inside of them. They technically do not have a heart, but a colorful orb that is embedded deep in their chest. It's their life source, and they are capable of reaching into their chest to retrieve the orb at will. It seems to be rather uncomfortable for them to do so though. For example, when the devils are trying to proove they're telling the truth to Konoe in one scene, Froud suggests a way to prove they're not lying. The other devils look rather unsettled at the suggestion, and no one jumps in to help with the situation. In the end though, Verg is the one who's forced to preform the act of removing his esscense.
The whole time this takes place, he seems to be straining to keep his composure, making grunting noises and sweating slightly, showing his discomfort.