Amen to Rot: Books One Through Four

It's a zombie apocalypse and Amen the creature awakens with amnesia. Amen has flashbacks from when he was human giving him clues on his purpose. He saves a thirteen year-old boy named Ace who is appreciably delighted to find a creature who eats zombies. Amen discovers there's sinister alien force at work, and these aliens are set on killing Amen. Amen remains one step ahead though, and he is discovering Ace is not just a survivor, but may be a key to fighting the aliens who brought on this zombie apocalypse.