I, the Purple-Robed Heavenly Master, Do You Want Me to Go Down the Mountain to Go to School?

After the first heavenly master of the human race signed a thousand-year non-aggression treaty with the Demon Emperor, he became an immortal with perfect merits and left a prophecy when he ascended to heaven. Thousands of years later, when the truce treaty between the two races expires, a young man will completely end the thousand-year grudge between the two races...