Parasyte -the maxim-
One night, a quiet invasion takes place. Across the world, mysterious parasites fall to earth and begin possessing humans one by one with the rest of humanity none the wiser. Shinichi Izumi is one such victim. But when his would-be invader fails to take over his brain and takes root in his arm, instead, Shinichi finds himself forced to share his body with a horrific creature that has a mind and an agenda all its own.