"The Art of Taming Immortals" meets the requirements of the question. I recommend it to you. The main character of the novel transmigrated to become the direct disciple of the sect master of a large cultivation sect. His master was righteous and his sworn brother was demonic. Through becoming sworn brothers with his big brother and taming the immortal beast, the protagonist struggled alone and finally succeeded. I hope you like this fairy's recommendation. Muah ~😗