Chapter 24

One Blow (一撃, Ichigeki) is the 24th chapter of the Parasyte manga series, written and illustrated by Hitoshi Iwaaki.

Overview
''Using his enhanced hearing to locate Satomi, Shinichi is able to rescue her. Meanwhile, the police begin their attack on Hideo. Although they manage to damage him, they suffer severe casualties. Shinichi decides that he's responsible for Hideo's rampage, and with the help of Migi, uses a rock to kill Hideo.''

Summary
Shinichi thinks about how Hideo looked and spoke like a human. He asks how far the parasite is, then focuses on his improved hearing to detect five students as well as Hideo by their breathing. He finds a group of three students nearby, one of them being Satomi, and asks Migi to hide. He tries to get the other two to evacuate with him, but because he had come through the carnage to get to them they panic, asking if he's human, and run away. As they turn the corner Hideo kills them.

Realizing his proximity, Shinichi picks up Satomi and jumps out down the hall, then decides against going through the carnage by instead kicking out a window and leaping out with Satomi in his arms and over a fence to get out of school grounds. He then hands her over to the rescue services, asking them to take care of her, and goes to kill Hideo.

Back in the school, the police have just come across the carnage and report it to their chief. They then notice Hideo across the hall.

Shinichi doesn't know what set Hideo off, but decides that because he and Migi knew about him being a parasite, it's their responsibility to stop him. Migi says that's strange, and the police should be able to stop him with only four or five deaths.

The first officer tells Hideo to freeze and is immediately killed, followed by the others behind him shooting Hideo. Although their bullets damage him, he doesn't stop. Migi tells Shinichi that bullets won't stop him—he has to be decapitated or have his heart destroyed to die, but he'll run out of energy eventually. Hideo stops and staggers up the stairs towards the roof, copiously leaking blood. Shinichi overhears the police chief. He asks if Migi thinks Hideo has sinned, and Migi states that is an arbitrary human measure. Shinichi picks up a large rock to finish Hideo off with.

A scientist in a lab gets a call from the head of Public Safety, Takizawa, and is told that they will have a parasite specimen soon. He hurries to head there.

Migi tells Shinichi that in order to kill Hideo they have to be 300 meters away at minimum to avoid being sensed, but can likely manage it if they combine their abilities. He heads up to the roof of a building while the police discuss Hideo's seeming unstoppability. Shinichi then wonders why Hideo, Ryoko Tamiya and A were born.

Hideo beings to exit the building and Migi morphs Shinichi's lower arm into a muscular mass as well as assisting with his aim. Shinichi throws the rock, which pierces straight through Hideo's chest, and he collapses, thinking Shinichi's name one last time. The police come out on the roof and surround his corpse.