User blog comment:Schiffy/Bleach Chapter 601 Review Podcast (real one)/@comment-24153155-20141021102009

Hmmm... about Nimaiya: I don't think it is that he owns a zanpakuto, but more that in a way he "owns them all". He may understand the soul of every blade he forges, and designs the blades accordingly. I think he is actually very decent at wielding a zanpakuto himself (he is a Captain after all), but he might not necessarily be the best Shinigami to wield zanpakuto-x to its best potential (that would be the Shinigami to which the zanpakuto is connected). Therefore, I think he might not require a shikai or bankai.

As for the zanpakuto he has wielded in the recent chapters, I think Nimaiya came in with the intention to kill Yhwach and co, and "Sayabuse" has an "evil blade": it doesn't discriminate its subjects, but needs to cut, there is no other "discussion" possible. It could be Kubo's version of a Muramasa nihonto. In that perspective, I could also understand why Nimaiya was thanking Yhwach and co.