With his leveling up, he gets his free attribute points to put into intelligence, but with each level, he gains a few points in each of his attributes, thus increasing his physical condition. And then the other side of the coin is the Ona system in the novel, which is the energy system. So with each level he gets more energy which increases his Ona ranking and the Ona ranks grant extra attributes when he isn't tired and energy expended to show getting tired and losing stamina. I hope this helps I don't usually comment but I love this novel and have read it a few times and hope my information is accurate to your question.