A Zanpakutō Spirit is a part of their Shinigami's soul, and their appearance and abilities are a reflection of this; as such, they also share their master's resolve. They exist in tandem with their master; they are born alongside their Shinigami, and die with them. A Zanpakutō Spirit's power is separate from that of its owner, and when a Shinigami draws on this power in addition to their own, their Zanpakutō will become even stronger.