Board Thread:Questions and Answers/@comment-31283382-20131221170348/@comment-10301320-20160624094651

That doesn't necessarily mean what I said is false. It's never mentioned how a soul becomes and Asauchi just that it does become one. Meaning there could be a container (i.e a physical blade) that the soul is placed into hence, trapped soul in sword. I'm not stating that as if it's fact though just a possibly, more than likely the soul is hammered into sword from or something *shrugs*.

There's next to no information about how Nimaiya makes these souls Asauchi since we've only seen him make an Asauchi into a proper Zanpakuto, which isn't even a regular thing as that process is supposed to take time for the shinigami to imprint his soul onto the Asauchi. Also regardless of if shinigami were willing to be turned into Asauchi, there at one point had to of been someone who wasn't willing, as that fate is likely to not be accepted by many on what is essentially a hunch as Nimaiya logically can't have had any proof that his process would create something like an Asauchi, given that it's HIS invention.