[Chaerys' Anime Review] Kiseijuu: Sei no Kakuritsu(Parasyte: The Maxim)

"You just do not notice that we are gifted just by being humans
We are absolute predators
We do not even have any enemies ,
Maybe there are other animals watching us
and thinking that someday 'We will beat them down'"
(from opening theme song)

All of a sudden, they arrived: parasitic aliens that descended upon Earth and quickly infiltrated humanity by burrowing into the brains of vulnerable targets. These insatiable beings acquire full control of their host and are able to morph into a variety of forms in order to feed on unsuspecting prey.
Source

Shinichi Izumi was one of the victims of these parasitic aliens, however, something unexplainable happened(actually it's not unexplainable, I'm just trying to create a little tension). Shinichi was able to stop the parasyte before it reached his brain, trapping the parasyte in his right hand. Due to this, the parasyte failed to take control of Shinichi's body, only able to control Shinichi's right hand. This caused a problem for both of them, because other parasitic aliens who have full control over their human hosts considered Shinichi's parasyte(now called Migi, meaning right) to be a failure, and sought to eradicate both of them. These events forced Shinichi and Migi to rely on each other in order to survive.