Board Thread:General Discussion/@comment-13237238-20130724132657/@comment-9941620-20140110183818

Zanpakto chose their owners, Tite never how or why they chose their owner, In the case of Toshiro, his choose 2 masters which is both rare and for one of them deadly. Also a zanpakto is the physical manifestion of a spirit, again Tite doesn't say what the spirits are or where they come from. They also have one and only one ability, it will get stonger as it's master gets stronger, it can not change type. Using Toshiro as an example, his is an ice type all of it's abilites are ice based though oddly as in the case of Rukia's zanpakto water is required to manifest their ice ability.