So the story start with a village boy in a certain village. What made this boy special is the he have "innate wisdom"="Reincarnate". His parents left him an inheritance a very ordinary bull. He grew with the bull and become a part time farmer but when he starts dreaming of his past life; He starts to yearn for adventure. Thats where he learned that his inheritance isn't simple as a bull. So that marks the journey to become a Demon or a Saint.
From the current chapter people might think his becoming OP but he is supposed to be due to him being a cultivator in a world of martial arts; It's just he cultivate the body and people tend to classify it as a martial arts training. (Difference is he cultivate the body using world energy rather than pumping up muscles.)