Based on Iwaaki Hitoshi's science-fiction horror manga by the same name.
The 17-year-old Izumi Shinichi lives with his mother and father in a quiet neighborhood in Tokyo. One night, worm-like aliens called Parasytes invade Earth, taking over the brains of human hosts by entering through their ears or noses. One Parasyte attempts to crawl into Shinichi's ear while he sleeps, but fails since he is wearing headphones, and enters his body by burrowing into his arm instead, taking over his right hand and is named Migi.
Because Shinichi was able to prevent Migi from traveling further up into his brain, both beings retain their separate intellect and personality. As the duo encounter other Parasytes, they capitalize on their strange situation and gradually form a strong bond, working together to survive. This gives them an edge in battling other Parasytes, who frequently attack the pair upon realization that Shinichi's human brain is still intact. Shinichi feels compelled to fight other Parasytes, who devour humans as food, while enlisting Migi's help.
Due to poor grades, Tsukune Aono, an average high school student, has been unable to get accepted into any private academy of his choice. By exceptional accident, the only school to accept him turns out to be anything but ordinary; the school is attended by youkai disguised as humans. Fearing for his life, he attempts to escape only to meet Moka Akashiya, a beautiful girl who just happens to be a vampire. Despite this, Tsukune decides to stay at the academy, hiding his human nature from students and teachers. Tsukune also discovers that when the rosary around Moka's neck is removed, her true nature emerges.
A new semester has arrived for Tsukune and the gang featuring a handfull of girl obsessed female first years and it seems like among these first years emerges another vampire who holds a grudge against her sister Moka. What shall this grudge lead to in the future and shall Tsukune suceed in taming this new problem child into his friend, no one knows what the future holds.