They start out looking something like this and then once they mature enough, they take on a more monstrous look like this. Each Greeed creates a certain kind of look for their Yummies, and they also reflect the desires that spawned them from their human hosts. There are six Greeeds and when they start taking each other's Cores the Yummies really started getting twisted.

Shingo is the name of the cop that Ankh borrows for most of the show. He's you typical normal police guy who happened to be in the wrong place and wrong time and got into an accident that would have killed him but Ankh needed a body in a hurry so he grabbed Shingo since he was near death. Being his host, Shingo actually gets better and such too, so it was kinda a mutual thing near the end.

TCH