Parasyte: Part 1 is a 2014 Japanese science fantasy action horror film directed by Takashi Yamazaki, starring Shota Sometani. It is the first film of the two Parasyte films, and was followed by Parasyte: Part 2. The films are based on the Parasyte manga series.
Mysterious aliens called "Parasites" suddenly begin their invasion when some of them infect humans by entering their brain. One of them attempts to enter the brain of high school student Shinichi Izumi, but resorts to infecting his right hand after failing to bypass his headphones. Thanks to this way of entry, Shinichi retains his human consciousness, unlike the other victims. After his initial shock, Shinichi befriends the parasite and names him "Migi" (Japanese for "right").
The parasites terrorize humanity by secretly killing them as sources of food. Shinichi himself has to fend against the parasites who are disgusted of the fact that his body exhibits two consciousnesses. One of the parasites also possesses Shinichi's teacher, Ryoko Tamiya; however, Tamiya is a lot more reasonable and is interested in studying the humans' way of life, which she does by becoming impregnated with fellow parasite Mr. A. Tamiya explains that despite having parasite parents, the baby she carries is a normal human.
When Mr. A's attack on Shinichi fails and results in his vessel's destruction, he transfers his consciousness to Shinichi's mother, Nobuko. Nobuko returns home and mortally injures Shinichi, although Migi manages to save him by using his essence to renew his heart, essentially infecting Shinichi's entire body with Migi's particles. Since then, Shinichi's personality starts to merge with that of Migi, namely, being apathetic to emotions; this results in Shinichi's estrangement from his girlfriend, Satomi Murano.