Parasyte, Vol. 1

Shinichi Izumi is an ordinary high schooler until a parasitic alien tries to take over his body while he sleeps — and only partially succeeds, ending up lodged in his right hand instead of his brain. Now sharing his body with "Migi," a parasite with its own voice and agenda, Shinichi has to survive in a world where other parasites are quietly replacing people around him, one head at a time.