Chapter 1

Invasion (侵入, Shin'nyū) is the 1st chapter of the Parasyte manga series, written and illustrated by Hitoshi Iwaaki.

Overview
''Snake-like creatures rain down from the sky and begin controlling human bodies. Shinichi has one of the creatures enter his right arm, but with no evidence, believes it to be a dream. After a confrontation with a gang, his arm comes to life and speaks to him. Elsewhere, the creatures begin to kill and eat humans.''

Summary
An unknown voice muses, "If the population were reduced to half, would fewer forests be burned? If there was one person for every one hundred now, would there be one hundred times less pollution? We have to protect the future of all life."

An unknown amount of spherical objects no larger than tennis balls rained down from the sky. As they landed, snake-like creatures emerged, and began moving about. They were in cities, parking lots, fields, trees, and streets. One of the creatures is seen being barked at by a stray dog. Elsewhere, another one of the creatures crawls under a door and into a house. It enters the ear of a sleeping man, causing him to shake and make strange noises. This wakes his wife up. She asks her husband if he's alright, but he then stops moving and falls back to sleep, so she does the same.

At another house, a single creature enters a window to the room of a teenager. Unable to enter through the ear due to the boy's earbuds, it tries to crawl in the nose. The boy, feeling the sensation, wakes up, pulls it out, and sneezes. Once he looks at it he throws it and jumps out of bed, believing it to be a snake, and prepares to kill it. While he is looking for the creature, it suddenly jumps at him and begins burrowing into his palm. As it moves up his arm, he begins screaming, alerting his mother and father.

Back in the boy's room, he's tied his headphones around his arm as a tourniquet, stopping the creature from moving further into his body but cutting off his circulation as well. His parents come into his room, revealing his name to be Shinichi, and ask what he's doing. He tells them about the snake that's burrowed into his arm and left a hole in his hand. However, when he goes to show them, the hole is gone. This prompts his father to ask if he's on drugs, which he vemehently denies and causes his mother to laugh. Confused, Shinichi begins messing with his arm. As his parents leave they tell him to go to sleep. Later, while sleeping he hears a voice declaring its failure. When Shinichi asks about the failure, he's told to shut up.

Shinichi then jumps awake, surprised by how soon the morning came. Downstairs, his father teases him and asks if he's found the snake yet. Shinichi mentions that his arm feels slightly numb, to which his mom says it probably due to the cord he'd wrapped around it. They then continued to have a regular morning. At a house ten kilometers away, the man from earlier is seen making faces in the mirror. His wife is heard sending the kids off to school, and then comments on her husband not being ready for work. She then asks if he wants anything to eat. The man walks over with a blank stare and grabs his wife, saying that she's food. His head then splits open into multiple sharp-toothed pieces and quickly bites down on her head, killing her.

At school, Shinichi is seen discussing last night's situation to a young girl. His teacher notices this and throws a piece of chalk at him, though his hand catches and crushes the chalk without him noticing. Embarrassed, the teacher hits Shinichi. Shinichi wonder why he got hit and one of his classmates tells him he made fun of the teacher.

His arm begins moving again without his notice, touching a female student on the back, then her face, which causes her to slap him. Shinichi asks why everyone is acting weird today. His friend then sees his stretched-out arm and freaks out, running away and telling him to stay away from him. After his arm returns to normal, Shinichi then asks permission from the school staff to go home because he doesn't feel well.

On the train home, he falls asleep and once again hears the voice declaring itself a failure. Waking up from this, he finds his hand touching another older student's face. The man's friends then surround him, asking him which school he goes to, and make him get off at the next stop.

Now in a public restroom, Shinichi tries to explain that his hand is acting weird. They ignore it and start hitting him, when his hand suddenly grows an eye. They demand his wallet and continue to beat him. His hand now has multiple eyes visible and thinks to itself, taking note of Shinichi's heavy breathing and blood pressure and concluding he's being attacked. Before Shinichi is hit once more, his arm slams into the attacker and sends him flying across the room. His friends, surprised by what they've just witnessed, decide to attack Shinichi all at once. Shinichi stands still while his arm again easily beats them all down, leaving only one standing, who hurriedly flees.

Realizing something is wrong with his arm, Shinichi quickly runs home. His mother comments that he's early when he arrives and is ignored, confusing her. In his room, Shinichi pulls out a knife, and asks what his hand really is. Suddenly he loses feeling in his hand, and watched as it split bleeding between his index and middle finger, changing into a creature with hands, eyes, and a mouth of its own. Stunned, Shinichi asks about his hand. The creature states that it ate it. Bursting into laughter and asking what this thing is, he tries to stab it. The creature easily stops and breaks the knife in half, flinging the blade into the ceiling. It then asks Shinichi to teach it how to speak.

Back at the other residence, the man is seen to have changed his face to match the new reporter on the TV and is echoing his words. When his daughter comes home, he quickly returns his face to normal and greets her. As he walks away, the chapter ends on the scene of the mutilated body of his wife.