Expanding on previous ideas: Wei Wuxian changed his profession to the legal system and traveled through time
The Patriarch of the Demonic Way versus the Necromancer
Xuanzheng·Baifengqiu
Fox, the nirvana phoenix, wandered to Baifeng Mountain. It only remembered the warmth of its owner Albus two hundred years ago. After rejecting the new owner again and again, it suddenly slipped out of Lan Wangji's palm.
Holding the fledgling chick in his hands, Lan Wangji suddenly excused himself amidst the greetings about the expansion of the hunting ground. He had a burning thought in his heart: This bird must be given to the person who gave him the rabbit back then.
Wei Wuxian made the bird's nest crookedly, but when he was drunk, he stuffed the baby bird into his pillow.
He fell into a dream before a thunderstorm: the old scholar told the history with many loopholes, and described the demon ancestor Wei Wuxian and Hanguang Lord Lan Wangji fighting side by side as ambiguous. When the children were asking about the whereabouts of the sacred bird Suzaku, Lan Wangji appeared from the dream mist.
Lightning ripped through the dusk outside the window, and the boy asked: "Is the Demon Ancestor really dead?"
The old scholar turned the pages of the book as if he were telling fortunes: "Heaven's secret..."
Purpose: The Patriarch of the Demonic Way versus the Necromancer