Parasyte -the maxim-

寄生獣 セイの格率

Shinichi Izumi, a seventeen-year-old high schooler in Fukuyama, wakes one night to find a worm-like alien burrowing into his right hand. The creature — which he names Migi — was meant to reach his brain and take over his body, but Shinichi's quick reaction trapped it in his arm. Now sharing a body, the two form an uneasy alliance: Migi handles combat with its shape-shifting hand, while Shinichi provides the human cover they need to avoid other parasites that successfully took human hosts and feed on people in secret.