Parasyte -the maxim-

Shinichi Izumi's life takes a turn to the bizarre when a mysterious lifeform attempts to infiltrate his body in order to snatch it, but it ends up stuck on where his right hand used to be and both are forced to cooperate. Meanwhile, similar incidents with gruesome outcomes start occurring in other locations.

Calling his new partner "Migi", Shinichi attempts to move on with his normal life despite his new condition, but other members of Migi's race keep coming after them to protect their secret.

Much to his dismay, Shinichi discovers that Reiko Tamura, a new teacher of his, is another inhuman just like those he faced before and knows his secret. However, Reiko is not interested in fighting him, and asks for his cooperation instead, but her partner, just called "A", has other plans.

Thanks to their teamwork, Shinichi and Migi defeat A, who ends up killed by Ryōko who quits school once news of her pregnancy reach her colleagues. Back at home, Shinichi's parents are suspicious of his behavior and he must make sure they do not discover the truth to ensure their safety.

Shinichi is targeted by a gang of delinquents and Kana, the girl who walks with them becomes suspicious of his nature. After returning home, Shinichi is caught by surprise when he is attacked by an enemy who possessed the body of his own mother.

After Shinichi is mortally wounded, Migi uses its powers to save his life, but weakening itself in the process. When Shinichi hears that his father is still alive, he rushes to the hospital where he is treated in order to protect him and enact revenge for his mother's death.

Shinichi meets Mamoru Uda, another human who is in a similar situation as him and they decide to join forces to protect his father. However, when the enemy appears, Migi falls asleep and both Shinichi and Mamoru must fight without its help.

Back to Tokyo, Shinichi's sudden change in behavior put his father and friends wary of him, and things get even more tense when Hideo Shimada, another parasite, is sent by Ryōko to keep an eye on him.

The recent events involving Shinichi draws him even further from his friend and crush Satomi Murano. Meanwhile, another of his friends gets close to danger after discovering Hideo's secret.