Spirit Rank (十殿阎罗) is a ranking system to rank a Requiem General's power.
In order to rank the Requiem General's, a ranking was set up. They represent the eight levels of hell. The higher level of the Guardian Spirit is, the higher the spiritual power will be and, the area they defend will become more important. In order to become a Requiem General, a person's power level has to be at the level of Sanjiva. In order to see Spirit Mail, a person's power level must be at the level of Kalasutra.