Ba and Ka
Ba (
Ba is necessary to channel Ka. When someone Summons or commands a monster, manifesting Ka, they use Ba. If a person loses too much Ka (such as by being killed or by losing Duel Monsters in a Shadow Game), this results in death and the Ba leaves the body (and may go to the Shadow Realm in the 4Kids Entertainment version). Likewise, loss of Ba (for example due to having one's soul siphoned or being harmed directly or indirectly in a magical Duel) damages the soul and the ability to maintain the Ka of Duel Monster spirits.
If people's Ba are separated from their bodies while they are still alive, such as when the Millennium Items steal people's souls, the bodies may continue to live but as soul-less vessels; such a body may even be taken control of by a new Ba. More than one Ba may inhabit the same body, too, such as in the case of Yugi and Yami Yugi (and Bakura and Yami Bakura).
The summoner's Ba influences the magical expression of Ka and therefore the kind of monster manifested by the individual, as demonstrated in the illustration on the top right of this page. A person's Ba can even fuse with a Ka to form an even more powerful spirit: such a union of Ba and Ka resulted in the birth of the Dark Magician.
In the anime, the current strength level of a DiaDhank user's Ba is shown on the Eye of Wdjat of the DiaDhank.
LP are a usually symbolic measurement of the would-be remaining Ba of a Duelist. However, during Shadow Games and magical Duels the relationship of Life Points to Ba and Ka is all too real; it also becomes possible for Duelists of strong mind and will to channel their Ba to increase or activate the powers of their monsters, not unlike infusing Spirit Energy into monsters but resulting in an expenditure of Life Points, or alternatively to increase their own spirit energy when used as Life Points by means of magical effects.