Parasyte -the maxim-

When ordinary high schooler Shinichi Izumi finds his right hand taken over by a sentient, parasitic alien, his life is irrevocably changed. This creature, which he names Migi, is one of many that have suddenly appeared on Earth, intent on burrowing into human brains and taking complete control. Unlike its brethren, Migi failed to reach Shinichi’s brain, forming an uneasy, symbiotic partnership that forces them to coexist. Now, Shinichi and Migi must navigate a world where grotesque, flesh-eating monsters walk among humanity, hidden in plain sight. As they encounter other parasites, the duo is drawn into a brutal struggle for survival, forcing Shinichi to confront his own humanity and the terrifying implications of his unique bond.

✦ AI-drafted summary