User blog comment:Xilinoc/Ch. 650 - THE THEATRE SUICIDE SCENE 4/@comment-24574959-20151105100214/@comment-26091912-20151109232925

What isn't clear though, is whether or not this is actually Nanao's Zanpakuto.

Shunsui's been a captain of the Gotei 13 for at least 200 years, and Nanao was most likely not even alive then; or at least an infant. So if that's the case, and assuming he's had both swords for the past 200 years, then there's no way it can actually be hers.

It probably belonged to her mother. Guess we'll find out next chapter.