The name of this anime show i saw on tv once

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So basically once when i was a kid i saw an episode or two of some anime on tv and i wonder if you guys could help me find out what show it was
What i remember was this one guy who seemed like a one-off character who had some sort of parasite in his body using him as a host, there was also a Flashback scene showing the parasite taking him as child, and also of it Killing a cat i think
I also remember this one Female character who wanted this other Characters arm, like she literally took of her own arm and put his there
The name and episode Numbers would be much appreciated, Thanks