You Said He Was the Son of Destiny, Just My Leek.

This is a world of immortal cultivation. In every reincarnation, a powerful demon cultivator will appear, and every time the demon cultivator is eliminated, the power of the entire universe must be combined. The protagonist Su Yichen traveled to this world, became a demon cultivator in this life, and obtained the Son of Destiny harvesting system. When the protagonist Su Yichen harvested all the male Destiny's Sons and slept with the female Destiny's Sons, he discovered the shocking secret of this world.