Manhua Variant: Name is changed to "Soul Sea."
A demon spiritualist can form a soul realm within their "energy center," or dantian. They are able to integrate captured demons within this soul realm and can then merge with their demon to gain strength and abilities greater than a regular fighter.
There are seven different types of soul realms. Each type represents a person’s unique personality and talents. By using a soul crystal an individual can discover their soul realm type, attribute, and form as well as the amount of soul force they possess. It is widely accepted that an individual's soul realm class determines their training potential. Chen Xiu claims that those with a red soul realm can not possibly reach a soul force greater then 600, which is equivalent to a 5 Star Bronze Rank.
Though it is true that some realms are more difficult to train than others, trainees of all classifications can obtain relatively high ranks if they train diligently with a suitable cultivation technique.
(according to Glory City)