Oh No, the Courtesan I Was Promoting Is the Demon Clan's Holy Maiden

This is a story set in the immortal realm, a place everyone longs to reach. In this world, a man named Ye Xuan accumulated a hundred lifetimes' worth of good karma in his previous life. As a result, he was reincarnated in the immortal realm as the heir of a Heavenly King. However, Ye Xuan had no interest in cultivating immortality, despite being the son of a Heavenly King. Instead, he was far more interested in lingering among the pleasures of the mortal world. At Mingyue Pavilion in the immortal realm, Ye Xuan spotted Liu Ruyan, an immortal who had ascended from the lower realm, and made her the top courtesan. What Ye Xuan didn't know was that Liu Ruyan was actually a Holy Maiden of the demon clan, with unfathomable strength. After his family suffered a devastating upheaval, Ye Xuan was forced to cultivate demonic arts and discovered Liu Ruyan's true identity. She then took him to the demon realm. Using Liu Ruyan's identity and the System within him, he fought his way to the top, becoming a great demon feared by all. In the end, he even led the demon clan back to the immortal realm, making the immortals who had hurt his family pay the price.