Shinichi and Migi square off against Mr. A in a fight for survival. With Reiko Tamura successfully getting pregnant despite being a horrifying flesh-eating monster, Shinichi is forced to confront his own changing humanity. And in the end, what it all says about human nature.

Shinichi comes in contact with another Parasite in the form of Reiko Tamura, a new teacher at his school. Unlike other Parasites who just want him dead, Tamura is more than content to merely observe Shinichi and Migi’s strange symbiosis, all the while holding the lives of his friends and classmates hostage. However when a third Parasite comes directly to Shinichi’s school to silence him, he must team up with Migi and stop it before it’s too late.

Resigned to his strange partnership with the parasite, Shinichi and the newly named Migi run into difficulty understanding each others’ vastly differing viewpoints and mentalities. Unable to accept that innocent humans are being slaughtered wholesale, Shinichi resolves to take a stand against the other parasites. Additionally, Shinichi himself begins to change…