Tu Xianyu allowed Ji Wuqing to survive for his own selfish reasons.
Ji Wuqing originally disappeared due to abuse of his powers, but he exchanged a piece of candy for his life.
Ji Wuqing: "I once suspected that she was a bad person who abused her abilities, but I was wrong. I was the bad person who abused her abilities."
[Silly hunter male protagonist & overall enlightened female protagonist]
Intention: Repay any favor you have received