Parasyte - An anime television series adaptation by Madhouse, titled Parasyte -the maxim- (寄生獣 セイの格率 Kiseijū Sei no Kakuritsu), aired in Japan between October 2014 and March 2015. Parasyte centers on a male 17-year-old high school student named Shinichi Izumi, who lives with his mother and father in a quiet neighborhood in Tokyo, Japan. The video below is a theroy on the parasites in the show.
If you haven't watched it already, you should probable watch it before you watch the video. It also says that before the theory begins 'π'.
I got that little bio from wiki and added in a few of my own words.