Manhua Variant: Name is changed to "Soul Power Strength."
This is a quantitative number that is representative of the strength and level of a demon spiritualist's soul realm. For new Cultivators it takes 100 units of soul force to rise a level, and 500 units to reach the next rank. The amount of soul force it takes to rise a rank gets progressively greater as the cultivator advances.
The soul force can be measured with a soul crystal. When soul force is injected into a soul crystal, speckles of light will form. Each of the speckles represents one soul force. Unused soul crystals are more sensitive and accurate. Not only can they determine the soul force but also the soul realm's form and attribute. However, soul crystals will have interference once when they are used more than once.
Another way of examining the soul realm is through using another person's soul force to examine the body, but even examining once uses up large amount of soul force. Even without using a technique, one can use their soul force to bombard another's soul realm directly. These types of uses are referred to as Secret Soul Techniques. If the soul force that is attacking is much larger then the one defending it can result in the defender's soul realm being destroyed. Without the soul realm cultivation of soul force is not possible, this completely cripples the person.