Kyūshī and Yōshī

Kyūshī (旧魂, "old soul") and Yōshī (幼魂, "young soul") are the terms used to refer to different kind of that dwell in the different dimensions. Kyūshī indicates a soul that has gone through reincarnation one or more times, while Yōshī means that the soul did not exist before its current life. Yōshī are a rare occurrence these days and while they are sometimes born into, they are prone to disrupting the spiritual balance and thus remain uncommon.

Typically, there is no difference between a Kyūshī or Yōshī - it was once believed Kyūshī have inherently more potential because their soul has gotten more opportunity to generate throughout their different lives, but the strength of  such as, who was a Yōshī himself, leads to believe this is largely a personal matter. When a soul travels between the physical and the spiritual plane, it loses all memories and abilities it has gathered during its life, with no way of recovery or recollection. The one exception to this process is Mūbiki, whose allowed him to extract the information hidden within his  and allowed him to retain everything of his former lives.