Angels and humans, shadows and masters, life and death are just separated by a dividing line. The soul of a dead person will make a wish, that is, he can designate an angel to come to the world to protect the person he hates the most until he lives and dies until the person lives out his life in peace. Such angels are called human shadows, and the shadow is dependent on its owner in life and death.
There is also a group of humans who can become angels through their own cultivation. Such people are called demonic monks.