Shunsui Kyōraku has two swords, remember?
but it has two spirits, and therefore it safe to say that it is actually two Zanpakutōs.
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those two are said to be; Katen Kyōkotsu
but i'm pretty sure that Shunsui called his bankai Sakuranosuke Ohana in the previous chapter.
and like all of us know; Nanao Ise does not wield a Zanpakutō.
but instead she's a Kidō Expert.
if i remember correctly though she keeps a sword concealed within her sleeve(?)
but she never used it in battle. which makes me think it's "just a random sword"
i believe that Nanao's mother made a pact with Shunsui, that she'd become his second Zanpakutō, if he promised to "take care of Nanao" or until Nanao was "ready" or something like that.
something tells me that perhaps Katen Kyōkotsu died while giving birth to Nanao Ise, and just before she died, she or Shunsui sealed her into a sword, and made a promise with Shunsui that "one day, she'll be Nanao's Zanpakutō