User blog comment:Silver-Haired Seireitou/Sake Time with Sei - Three's a Crowd/@comment-24384232-20150517233800

My thoughts on the matter tend to drift off the beaten path with regards to Zanpakutou. I've of the mind that the Zanpakutou, the Shinigami's Inner World, and the Well of Souls or Great Wheel (essentially the cycle of reincarnation, and all the spirits that reside there) are connected.

But to answer your question, I dont think anything would change. I think you'd have multiple swords, all with the same spirit. Ill explain my reasoning:

I am of the belief that the Zanpakutou serves as a conduit, a key if you will that serves to connect the Shinigami's Inner World, which serves as the bridge to the Well of Souls. This Well, is for a lack of better term is the ... place? Dimension? Whatever, its where the souls of the deceased go before they reincarnate. Its a dwelling place that sits between life, and death.

The Inner World is where the Soul resides, the Zanpakutou simply facilitates the resonance (the release states) necessary to bridge the gap between you and this soul. In this respect, what an Asauchi is and what it does is ... somewhat different, then what is obviously implicated by the description.

I theorize that there are potentially an infinite number of spiritual realms, connected by transient realms which can only be accessed empathetically. Meaning that to enter said realm you must empathize or spiritually embody some aspect of that realm. Distance is a physical measurement, and in a spatially infinite world based on the idea of will and spirit, then the logical step is the empthatic distance once has to said realm. With that in mind, an Asauchi or the Zanpakutou it becomes act as a means of facilitating that empathetic link, using the Inner World of the Shinigami as the bridge to connect the Shinigami and the spirit in question.

The spirit itself is unique. Within the Well of Souls a soul exists but it also does not exist yet. Think quantum mechanics, there are an infinite number of observable states, but if you observe one, all the others collapse. Following a similar line of though the same would apply here. The spirit that resonates with you is one that is has already existed, but only emerges when this connection is formed between the Shinigami and the Soul Companion.

This would also imply that its possible to bond with spirits that have existed before, gods, or other divine creatures such as Dragons, Kitsune or other beings. Even once famed swordsman like Miyamoto Musashi. Actually I wouldnt be surprised if that was the case, given the Shinto beliefs and their tendency to enshrine historical figures who have been elevated to the status of kami. After-all, Tenjin was originally a scholar who on his death became a kami.

Having explained that, whether you had one zanpakutou or multiple ones, it doesnt matter, the Zanpakutou itself is simply a tool that facilitates the resonance necessary to bridge the two spirits into one. But Shunsui's zanpakutou is a rather interesting one. Being able to resonate with two spirits? Even similar ones? His nature must be very... fluid to allow such a thing. Not that I'm surprised given the personality he's shown so far.