What is the ending of "Tian Wu Ji" about?

A hundred years ago, Shi Xingyu, the king of the Stone Kingdom, commanded four divine dragons, who were unrivaled in the world. He is known as the Four-pole Dragon God. Shi Xingyu fought in all directions and almost unified the fifty countries of the Western Regions under his command. However, he finally fell into the devil's path and became a murderer. For a time, countless small countries were wiped out in one night, the sand was stained with blood, all life was reduced to ashes, and the fertile land of thousands of miles almost turned into a purgatory. As a last resort, the elder of Moyun Academy, Old Man Ziji, ordered his disciple Jun Qianshang to use the forbidden power of reincarnation to defeat the Four-pole Dragon God, but he still could not eliminate it. Old Man Ziji used the technique of fractal suppression to divide it into five parts: heart, spirit, mind, form, and body, and imprisoned them in the supreme secret realm. Since then, the name of the fourth-level dragon god has become a secret demon taboo, which is passed down throughout the world. Moyun Academy is the first academy in the Tang Dynasty. The owner of the academy, the old man Zi Ji, has attained the highest level of cultivation. On the day of the academy's selection of students, Master Xueyin and Da Ri Zhi, who are equally famous as Zi Ji, came hand in hand to exchange for the supreme rare treasure. I just ask Ziji not to accept any more disciples now. Because the gods and Buddhas have made a prophecy, one of the current students of Moyun Academy is destined to trigger the restriction and release the King of Demons. At this time, the Four-Pole Dragon God will be born again with endless resentment against the world. The prosperous age of the Tang Dynasty will surely end because of this, and all living beings will surely enter purgatory again. However, old man Ziji ignored the two people's obstruction and continued to open the hospital and select disciples on the grounds that his destiny was irreversible. It's just that the selection results of this batch of students were beyond everyone's expectations. The first apprentice recruited by the academy was actually a wandering gangster - Li Xuan. Li Xuan was uneducated and had no skills. He just entered Moyun Academy by mistake, and inexplicably became the senior brother and enjoyed many privileges in the academy. Li Xuan does not seek advancement, and does not use these privileges to practice Taoism. Instead, he explores and travels around, and by the way completes all kinds of weird and dangerous love tests for him by Su Youlian, the concubine in the courtyard.

While Li Xuan was spending his days leisurely in the academy, playing the world with cold jokes, Master Xueyin, the demonic leader who was as famous as Zi Ji, found him. He was promised a lovely wife, a beautiful concubine, and immense wealth, as long as he left Moyun Academy.