Parasyte

Kiseijū (寄生獣, Japanese: "Parasitic Beasts"), known in English as Parasyte, is a horror story about tiny parasitic worms that infest humans and take over their brains, assuming complete control of the host and an ability to shapeshift freely. But one particular Shinichi Izumi avoids complete infection, instead having the parasite take over control over its right arm only, leading to a strange coexistence.

Status

Anime: incomplete. (14 episodes)

Thoughts

In most conventional areas of judgment, Parasyte is probably about average at best, so I don't recommend the anime unless it's your thing. It takes a peek at the morality standards humans set for themselves and other beings, but doesn't really go too far with the questioning.