I Thought It Was the Tang Dynasty, but It Turned Out to Be Journey to the West

The protagonist, Su You, transmigrates to the Tang Dynasty. His predecessor died after a fox spirit drained his yang energy, and Su You discovers that demons and ghosts are everywhere in this world. That is why the Tang emperor sent Tang Sanzang on his pilgrimage to the West, hoping to purify the realm. After acquiring a pay-to-get-stronger System, Su You chooses to spend his way to power. He keeps the beautiful ones for himself and kills every last ugly one.