Heaven and earth are divided into three realms: Yangjian (human world), Yinjian (underworld), and Tianwai (the realm of chaos beyond reincarnation).
The balance of the three realms is maintained by the law of yin and yang - the Yang world is full of vitality, the underworld accommodates the souls of the dead and circulates reincarnation, and the outer world is the primitive chaos where yin and yang have not yet differentiated. The sun is not only the source of light in the yang world, but also the hub of the law of yin and yang: when the sun rises, yin retreats, and when it sets, yin advances. The alternation of day and night is the external manifestation of the flow of yin and yang.
The underworld is not a simple "place", but a huge dimension with ten halls of Yama, each leading one side and co-ruling reincarnation. The ten halls are connected by the River Styx, where judges, underworld agents, and ghost officials perform their duties. There are eighteen layers of hell to punish sinful souls, a city of unworthy death to accommodate those who died abnormally, and a well of reincarnation to push souls into the next life. The entire underworld is a precision-operated "management system for the dead."
