Midori no Hibi, Kiseijuu: Sei no Kakuritsu Recommendations
Midori is the EVEN MORE bizarre romantic equivalent to Parasyte's grotesque parasitic broship. They present the same problems - namely, how it's too awkward to masturbate with a talking hand - but go about them in very different ways. One involves a lot of death; the other involves a lot of love.
The 'hand' in Midori is more like a female talking hand-puppet that JUST HAPPENS to be joined to the lead's arm one morning when he wakes up... and is the girl the lead has a crush on, ofc. On the other hand, Parasyte has a transforming alien life-form that, initially, had every intention
A teenager wakes up and discovers that his right hand is no longer what it used to be ...
In Midori no Hibi, the teenager right hand becomes his waifu
In Parasyte, the teenager right hand becomes a 'parasitu'
A symbiotic relationship between parasite and human exists in both anime.
Coincidentally, both take place with the protagonist's right hand. But in the case of Midori no Hibi, the so called parasite is an actual girl. Whereas in Kiseijuu, it is an actual parasite.
Both have to learn to adapt the current odd situation that either of them have no actual idea how they ended up in.
Having ano0ther entity occupy your hand concept. While Kiseijuu is darker midori no hibi is more light hearted.
Both involve hands being taken over by an entity & changing shape. Both awesome too.