Himizu's Sometani Shôta stars as high-schooler Izumi Shinichi, a typically moody teenager dealing with the usual problems of girls and school while living at home with his single mother. The world changes overnight when a newt-like alien organism appears on earth, entering into the brain of its victims and taking control of their bodies. When one of these organisms finds its way to Shinichi's bedroom, the parasitic takeover does not proceed as expected. Earplugs blocking the favored ear-canal entrance point to the brain, the slippery organism finds its way in through the boy's right hand. With a hastily fashioned tourniquet preventing the creature reaching the target grey-matter, it instead takes refuge, and control, of the limb. Unlike other victims, Shinichi retains his brain function while the parasite develops into a cute one-eyed being that rapidly absorbs information in order to learn how to survive on earth. While other infected humans take to devouring the people around them before gradually becoming organized for global takeover, Shinichi's alien inhabitant needs his host to survive. Bound together, the uneasy partners must come to terms with their predicament while simultaneously dealing with the hostile aliens around them and the threat to friends and family.
After introducing the young protagonist and the rest of the supporting human cast, caring mother Nobuko, (Kimiko Yo, Departures) and schoolgirl love-interest Satomi (Hashimoto Ai, Adult Drop, Sadako 3D), the plot quickly concerns itself with the story's alien inhabitants. Early scenes take the comedy route as Shinichi loses control of his body in a way that's far more unusual than that faced by most boys his age. Things get seriously weird when his hand sprouts a mouth and eye and begins to talk. The being that emerges is named Righty, (voiced by Abe Sadao) whose straight-talking calm contrasts with the emotional teenager, who is understandably disturbed at the sight of his body twisting into impossible shapes and contortions. The parasite needs to learn about the earth in order to survive, and is accepting of the fact that the two are now a team, if one dies, so does the other, and Righty's primary goal is survival.
Director Yamazaki Takashi gained visual effects experience on the CGI heavy Space Battleship Yamato and he again took charge of FX duties here. Parasitic takeover leads to amusingly grisly results with heads contorting into giant teeth-filled mouths fit for devouring former family members and lashing out with whip like blades during battle. The effects are best when at their strangest, unfortunately Righty falls victim most to an overly polished CGI look (reminiscent of Red Dwarfs' Vindaloovians, though not as fun). While the blood really flies during alien attacks, after an initial encounter with a fellow parasyte the action slows down considerably. Other symbiotes appear in the form of a new science teacher who views Shinichi and Righty as an interesting lab rat to be kept around for observation, and more immediate threats including a creepy fellow student and a former policeman who has no interest in letting the half-human abomination live. Lengthy and unnecessary scenes of exposition, many of which somewhat bizarrely take place in an aquarium complete with manatees floating in the background, really put the breaks on the immediacy of the takeover. As stories of this kind have been hitting cinema screens for decades it's not hard to grasp the direction the film is taking so scenes of the largely emotionless brain parasytes conversing are unnecessary. While it is interesting to see the differences in each of the creatures, and the changes taking place within Shinichi, this middle section drags while it establishes characters and future plot strands, sacrificing this film's structure for payoffs in part 2. Shota Sometani is a capable actor adept at this kind of role well but his moody and permanently stroppy teenager doesn't make for the most likeable or charming of protagonists so the upcoming charisma boost offered by alien politicians Kazuki Kitamura and Tadanobu Asano is much needed.
Parasyte waits until the end to kick into gear, finally delivering on the promise of bizarre alien action and global-scale menace promised from the outset. A bloody school slaying leads to an emotionally charged ending as Shinichi is forced to perform a final act that carries a heavy psychological burden. Utilizing his new abilities to contort into a living weapon and going up against similarly powered adversaries the action is ramped up while putting the pieces in place for the concluding chapter.
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. If Part 2 can match it the excitement and visual spectacle of the films final third then this character led build up may yet be justified.