I Was Born Among Cavemen, but My Knowledge from the Future Made Them Unstoppable

In this world, humanity lost a war against the magical races and now occupies the lowest rung of society. The protagonist is reborn as an ordinary human and discovers the ability to copy one trait from each monster he defeats. After defeating a weak beast, he gains enhanced vision; after another, increased regeneration; after a third, protection against magic. Gradually, the hero begins to combine dozens of abilities, becoming a being that cannot be classified as belonging to any known race. He creates a secret refuge for fugitives and begins to liberate human settlements. But the world’s most ancient rulers learn of an ability they believed had been destroyed thousands of years ago.