I gain power by absorbing monsters

Isaac was just an ordinary man, with no great future ahead of him, and one night he died a miserable death. Yet one day, light replaced darkness and he found himself in the body of a young boy in a frightening world. Humans are at the bottom of the food chain, hunted by ferocious beasts and despised by other races for their weakness, their extinction is near. Isaac has only one goal: to become stronger in order to survive.