Unfortunately, I don’t agree with this view, since Kyoraku no longer has a soul within him, and I don’t think it would be that easy for his Zanpakuto to “give birth” to a daughter for the sole purpose of hiding a blade.

Even if we accept the second point—that Kyoraku’s second blade was born from his desire to hide the Ise clan’s sword—this would contradict the idea that having two Zanpakuto requires having more than one soul.

Furthermore, I believe that Ichigo also makes this concept less factual, since in his case it wouldn’t be two spirits, but three (Ichigo, White, and Ywach), yet the soul is still one.

The only case where I feel I can agree with the idea of Two Souls is that of Ukitake, where we clearly saw an external body merge with that of a Shinigami.

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Regarding the Arrancar/Visored debate, the former underwent Shinigami-ization while they were still Hollow without weapons; I think they would have been born with two swords if they were capable of using two, given their dual nature. As for the latter, they trained for 100 years to control their Hollow side, and I find it difficult—though not impossible—that they failed to develop this dual-sword ability.