One night, a quiet invasion takes place. Across the world, alien beings, known as Parasytes, fall to earth and begin possessing humans one by one with the rest of humanity none the wiser. Shinichi Izumi is one such victim. But when his would-be invader fails to take over his brain, and takes root in his arm, Shinichi finds himself forced to share his body with a horrific creature that has a mind and an agenda all its own.
On a quiet night, unsuspecting high school student Shinichi Izumi is attacked by an alien creature that burrows deep into his right arm. The next morning, Shinichi comes to learn that this being, known as a Parasyte, is now a part of him.
Shinichi and his Parasyte, now named “Migi,” battle for control of Shinichi’s arm as the number of Mincemeat Murders increases. But when an encounter with another Parasyte turns hostile, they must work together if they hope to survive.
With the number of murders growing by the day, a new Parasyte appears at Shinichi’s school, posing as the substitute teacher Ryoko Tamiya. Shinichi must learn if she is friend or foe before his classmates are put in danger.
After the events involving Ryoko, Shinichi and Migi are slowly adapting to one another. But the closer Shinichi grows to Migi, the further he drifts from his family as he struggles to keep them from discovering his secret.
A violent confrontation with a gang brings Shinichi face-to-face with a girl named Kana, who begins to take an interest in him. Shinichi’s parents continue their vacation, but their trip is cut short by an unexpected attack.
With Shinichi at the brink of death, Migi takes drastic actions to ensure his host’s survival. After a trying recovery, Shinichi learns that his father is still alive and races to his side before the Parasyte that attacked his mother strikes again.
Shinichi sets out for revenge and runs into an unexpected ally. Together they team up to take down the Parasyte that brutally attacked Shinichi’s family. But when Migi falls asleep, Shinichi is forced to engage the enemy on his own.
Life has returned to normal, but Shinichi has not as his ties to Migi continue to change him. As those around him grow wary of this ‘new’ Shinichi, a Parasyte named Hideo Shimada emerges from the shadows and begins attending Shinichi’s school.
The divide between Shinichi and Satomi continues to grow. Shinichi’s classmate, Yuko, investigates Hideo and unknowingly stumbles upon a dangerous secret. Meanwhile, Ryoko Tamiya, now known as Reiko Tamura, plots behind the scenes
The confrontation between Yuko and Hideo comes to a gruesome head when Hideo goes on a rampage throughout the school. With Satomi missing, Shinichi must hurry and find her before Hideo can get to her first.
Kana’s interest in Shinichi transforms into full-blown obsession when she discovers that she is able to sense his presence. Little does Kana know that it isn’t Shinichi she can sense, but something much, much darker.
Shinichi finally decides to reveal his darkest secret to Kana in an attempt to protect her from the danger she has unknowingly placed herself in. However, Shinichi’s actions have unforeseen consequences that end in tragedy.
In the aftermath of loss, Shinichi struggles to feel anything but indifference and begins to question his own humanity. He soon realizes that he is being watched when he discovers a private detective following him.
The private detective, Kuramori, discovers Shinichi’s secret and flees from him. Concerned about Kuramori’s intentions, Shinichi seeks help from Mamoru in order to track him down.
Although he still has his doubts, Kuramori reluctantly decides to help Shinichi hunt down Reiko and her group of Parasytes. But when a strange man appears, Shinichi soon goes from the hunter to the hunted.
A powerful Parasyte unlike any Shinichi has ever seen before attacks, and soon Shinichi and Migi are running for their lives. Meanwhile, Kuramori’s search for the truth puts his family in harm’s way.
After Reiko’s judgment is called into question, three members of her own group seek to eliminate her. With Reiko otherwise occupied, Kuramori takes advantage to seek revenge for his family.
With her feelings regarding humanity and the purpose of Parasytes now in question, Reiko encounters Shinichi and Migi one final time. When police arrive on the scene, Shinichi soon finds himself at the center of their attention.
Investigators continue to hold Shinichi, certain that there is something he is hiding. In an effort to uncover his secrets, they soon bring him face-to-face with the serial killer, Uragami, who has a unique ability.
The police commence their operation to take out Hirokawa and the remaining Parasytes. However, plans go awry when the Parasytes attempt to fight back. Things take an even more gruesome turn when Gotou appears on the scene.
In the chaos of the raid, Gotou escapes and vows to return to kill Shinichi. Plagued by fear and with nowhere left to run, Shinichi turns to Satomi for comfort.
Shinichi decides to take Gotou head on, and tracks him to a remote area to fight him. When the battle goes awry, Migi makes an unexpected sacrifice.
With Migi no longer at his side, Shinichi attempts to take on Gotou by himself one final time.
After Migi says his final farewell, it seems like Shinichi’s life can finally return to normal until an unexpected enemy resurfaces.