Say, Aria. Have you've heard of this anime called "Attack On Titan"? It's about a bunch of humans who are trying to defeat these strange gigantic creatures that eat humans (humans only. They spare the animals and it hasn't explained why yet).
Anyway, one of the main characters, Eren, gets eaten by one and the next thing he knew, he woke up as one of the monsters, but still remained his consciousness. He can turn back into a human at times, but sees his new powers as a way to not only find out where why and how the titans came to be, but vowed that it'll be the humans that'll be devouring THEM.