Mysterious and brutal murders begin to take place on Earth. People don’t know it, but it’s caused by some kind of pest that happened. Gradually they begin to possess humans by penetrating through their ears and nostrils, adhering to their brains.
One of these parasites named Migi can only control the right arm of a high school student named Shinichi Izumi, and no matter how hard he tries, he can’t completely overpower him. Over time, the two learn to co-exist and fight off other parasites that view humans as mere food.