Shikonjin

Shikonjin (四魂人, "Four Soul People") are that possess distinct characteristics from all four major spiritual races known to the ; namely,, , , and. They are considered to be divergent entities that do not conform to the restrictions of any particular individual existence, affording them the greatest possibility of becoming. The existence of these Shikonjin are so rare that even the number of in any given era outnumber them, deeming many to disregard them as being impossibilities. It appears that beings such as these are the most suitable candidates to replace the in the event of his demise; such was the case when  killed the previous King, and, a known Shikonjin, was briefly considered to become the new Soul King in his place. also ventured a pursuit to turn, being an artificially created Shikonjin, into the Soul King.