I Parasitized a Hundred Hosts

The parasitic creature Sinner was resurrected in the world through the body of a former weirdo researcher. What awaited him was actually... A city infested with monsters! An adventurer with a system! And a greedy crow that ate its own flesh and became a parasite! In order to survive, he can only re-train his body from scratch by traveling through various worlds. Is it a new body acquired through continuous development? Or choose to develop a better body? Or is he parasitic in the adventurer's body and letting him work for him? Why can't we have them all? (Non-human protagonist, infinite universe, original world)