Parasitic aliens suddenly invade Earth, taking control of human brains to feed on unsuspecting prey. Sixteen-year-old Shinichi Izumi becomes a victim when one parasite attempts to take over his brain but ends up in his right hand instead. Unable to relocate, the parasite, named Migi, must rely on Shinichi to survive. Forced into an uneasy partnership, the two must defend themselves from other hostile parasites intent on eradicating them. As they navigate this dangerous new world, Shinichi and Migi struggle with their growing connection while facing threats that could destroy humanity.