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.
Meanwhile, an underling of Tamiya, Takeshi Hirokawa, runs for mayorship in order to set up the town for the parasites' interests. Another parasite, Hideo Shimada transfers to Shinichi's school and initially acts friendly, but when a student discovers his true identity, he massacres the students. Shinichi is able to kill Shimada, who is left to his fate by Tamiya due to a disfigurement that Satomi causes, which makes him unable to control himself. Tamiya gives Shinichi the location of the Mr. A-possessed Nobuko before leaving the scene. At their meeting, Nobuko is able to overcome her parasite's consciousness long enough for Shinichi to safely kill her.
The epilogue details Hirokawa's successful run for mayorship, the appearance of the mysterious parasite Goto, as well as Shinichi's visit to Satomi at the hospital, where an unknown individual records him talking with Migi.
In 2005, New Line Cinema had acquired the film rights to Parasyte in 2005,[4] and a film adaptation was reported to be in the works, with Jim Henson Studios and Don Murphy was set to be in charge of production.[5] New Line Cinema's option expired in 2013, prompting a bidding war in Japan. Film studio and distributor Toho won the rights.
The film topped the box office on its opening weekend in Japan, earning $2.9 million from 256,000 admissions on 418 screens.[7] It grossed around 800 million at the Japanese box office after two weeks.[8] The film grossed CN48.3 million at the Chinese box office.[9]
Mark Schilling of The Japan Times gave the film 3 and a half stars out of 5, saying, "I couldn't call myself a fan of the manga, but the film adaptation of Parasyte hits the hard-to-find sweet spot between black comedy and serious sci-fi/horror".[10] Peter Debruge of Variety in his favorable review felt that "[the film] marks an entertaining new iteration in the body-horror category, as if someone had grafted a very dark high-school comedy onto a David Cronenberg movie."[11] Meanwhile, Christopher O'Keeffe of Twitch Film in his unfavorable review commented that "Parasyte: Part 1 spends a great deal of time laying the groundwork for the concluding chapter and its charmless aliens and the scarcity of action in early scenes fail to make it stand on its own."[12]
The police use serial killer Uragami to identify parasites among humans, as he has a special ability to detect them; however, he is unable to correctly identify Shinichi Izumi. A few months after the events of the previous film, Shinichi continues to track down and kill the parasites who terrorize the human world for food, with help from Migi, the parasite that infects his right hand. He learns that he is being tracked by Shiro Kuramori, a reporter hired by parasite Ryoko Tamiya. Shiro discovers the truth about Migi, and plans to expose Shinichi. Shinichi tells Shiro that Tamiya is a parasite, and urges him to stop getting involved for the sake of his safety. Tamiya meanwhile, has given birth to her human son and slowly learns how to become a mother, growing furiously protective of her baby and killing her fellow parasites when they threaten him.
Despite Shinichi's warning, Kuramori goes on to record his conversation with mayor Takeshi Hirokawa, who secretly heads an organization composed of parasites. Hirokawa orders the parasites to kill Kuramori, but they are only successful in killing his daughter. Swearing revenge, Kuramori kidnaps Tamiya's son and calls her to a park so she can see him kill the baby. Despite Tamiya and Shinichi's attempts to convince him otherwise, Kuramori almost goes through with his plan, resulting in his death at Tamiya's hands. When Tamiya then approaches Shinichi, the police fatally shoot her. Instead of defending herself, Tamiya protects her child, explaining to Shinichi that she now knows what it is to be human. She hands her son over to Shinichi before dying, reminding Shinichi of his own mother.
At the same time, a secret service team evacuates the town hall upon discovering Hirokawa's true alignment. They are able to kill nearly all of the parasites as well as Hirokawa himself, who turns out to be a human who supports parasites and distrusts humans. The remaining parasite, Goto, turns out to be too powerful for the team, as his body contains five parasites. He massacres the team and begins his pursuit of Shinichi. Cornered at a forest, Migi sacrifices himself to allow Shinichi to escape.
Shinichi mourns Migi and is comforted by his girlfriend, Satomi Murano. The next morning, Shinichi discovers that a part of Migi is still in his right hand, thanks to his body being infected with Migi's cells in the previous film. He lures Goto to a disposal facility and is able to fatally injure him. At first reluctant in killing him, Shinichi ultimately decides that he wants to protect his loved ones, and finishes Goto off. Back home, Migi tells a dismayed Shinichi that since the parasites have died down, he will now go into hibernation to achieve an evolution, presumably up to the point where the two will never see each other again, breaking Shinichi's heart.
A few years later, Shinichi and Satomi visit the now toddler son of Tamiya, who is named Taiki Tamiya. Afterward, Uragami appears, kidnaps Satomi, and takes her to a roof. He states his belief that humans are the real monsters and asks for Shinichi's opinion, since he is certain that Shinichi is a parasite. However, with Satomi's encouragement, Shinichi defies Uragami's opinion and successfully saves Satomi with help from Migi, who had momentarily awakened from his dormant state to help him.
Edmund Lee of South China Morning Post gave the film 2 and a half stars out of 5.[3] Elizabeth Kerr of The Hollywood Reporter described it as "a prime example of filmmakers, production houses and distributors hoping to squeeze one more box office hit out of their source material that doesn't always demand it, the net result being a struggle for content".[4] James Marsh of Twitch Film felt that "[the] sci-fi, horror and adventure elements of the story are all sidelined here, and the result is a fairly underwhelming experience, albeit one retaining glimpses of scattered promise and invention left largely unrealised."[5] Mark Schilling of The Japan Times said, "the message is that humans and parasites are both living products of the same indifferent universe, facing many of the same survival problems, if not solving them the same way."[6]
There is much implied here about truth and falsity. The structure of the fake documentary seems to grow naturally out of the figure of Mlis at its heart, the man who took a tool that seemed as though it could reproduce at least the appearance of reality and showed how it could be used as a tool of the unreal. La Rage reminds us that Mlis, the stage magician, began his showings by assuring the audience that what they were about to see was not true; that this was the era of audiences fleeing the projected image of a moving train. In a sense the whole film is a Mlisian fable in more than one sense, with Mlis not just subject but inspiration.
It certainly worked for the Hall crowd, who gave Adam Nimoy a standing ovation when he came out for a post-film discussion along with his producer David Zappone (the following comes from handwritten notes I scribbled as they spoke). Nimoy answered questions about the difficulty of the process of making the film, saying that finding the balance of himself, his father, and Spock was difficult with much editing work needed. He abjured the auteur theory at least for this film, insisting on the importance for him of his team of collaborators. On the other hand, he did find that people at Paramount were eager to co-operate with the production for the sake of Leonard Nimoy, letting him use video clips and music. The trick to distilling his material, he found, was to focus on the story of the film. Nimoy said that the movie, 112 minutes long in its final form, never exceeded two hours in any cut they tried.
Asked about the character of Spock, Nimoy said that his father had loved Spock, often reminding him that Spock was the only alien on the bridge of the Enterprise. The more specific you are in your art, he said, the more universal you become, and Leonard Nimoy had been very specific in who he was. To another question, producer Zappone said they could not have made the film without Kickstarter, which let them work without studio interference. The film drew 10,000 backers for the campaign, a record for Kickstarter backers.