Help! Please!!!

Can anyone tell me the name of this manga...

I'm trying to find a manga about a 'boy.' It starts out in a dungeon where its a body-less spirit that can see spots or wholes at the back of creatures heads. They jump bodies a few times, saving humans every so often - once as a bat and dog. They eventually leave the dungeon in a cats body. This keeps happening as the main character journeys around till they find this like mad doctor that summons a humanoid boy for them.

Thanks!