Absorbing an other Being's or Spirit's Soul improves the powers and may allow Ascension. However, if the absorber is a Being and the absorbate a Spirit with equal power, the Spirit overpowers the Being's mind and ascends immediately beyond the usual strengths. A Spirit with godlike powers is born. An Aspirant.
In their reference as Possessed, Aspirants are often considered a possession of the Being by the Spirit that can be exorcised.