The heart disease brought out by An Xue Niang in the womb caused her to die at a young age, but she was unwilling to do so. After she died, her soul's obsession was "I want to live", and she became a demon because of this.
She became a demon and was imprisoned in purgatory by the interface guardian. The existence of this purgatory was to eliminate the demon's obsession.
Let's see how An Xue grows into a peak existence in purgatory.
Purpose: No matter how difficult life is, I will live