The Bounts' inability to age is a product of how they survive: consuming Human, Shinigami, Hollows and Quincy souls which potentially increases their abilities. This also seems to make them infertile, as only one Bount, Yoshino Sōma, had the ability to reproduce out of the entire species. Normally, Bounts consume human souls that have already died.
Dolls
Bounts, being created as variations on a Shinigami soul, have similar powers to Shinigami. The foremost of these powers is the Bount doll, a familiar equivalent to the Shinigami's Zanpakutō. Like a Zanpakutō, a doll is its creator's power given physical form. Also like a Zanpakutō, a doll's personality is much like its creator's, though the dolls seem to have more personality variation than the Zanpakutō spirits seen thus far.
The main difference between a doll and a Zanpakutō is how they operate. Unlike a Zanpakutō, whose personality is generally dormant except when the Shinigami wishes to speak to them, a doll's personality is always dominant. Dolls are self-sufficient when released, though they can easily be resealed. The Bounts' ability to control their doll is largely based on their individual power and relationship with the doll. Moreover, if either the doll or its Bount partner sustains severe damage in a battle, the Bount may lose control over his doll, depending on the amount of damage dealt. If a doll is injured, it will simply return itself to its sealed state. However, should its master be injured, the doll may go berserk and kill its master, as Ugaki and Mabashi's dolls did. A doll may also kill a Bount who is not powerful enough to contain it, as was the case with Cain. Bounts with a genuine bond with their dolls can transgress this (but only if their interaction goes well beyond that of between master and slave), however, as shown by Yoshino's doll's loyalty towards his master to the point where he refused to leave her side to fulfill her final wish: for her to be merged with him.
Like a Zanpakutō, dolls are generally sealed into an object and released as necessary (Gō Koga's doll, for example, is sealed into a metal sphere but Hiddan doll is merged with him by his special abilities). The object varies greatly from person to person and is often an expression of the doll's abilities. In order to call upon a Bount's doll, the phrase "Zeige Dich" is said, which is a German phrase meaning "Show yourself."
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Subject: Bounto Dolls & Powers 
