User blog comment:Xilinoc/Ch. 650 - THE THEATRE SUICIDE SCENE 4/@comment-4207271-20151105081603

That explains why in the filler arc they were so weird about eachother... it's not because Kyokotsu didn't like Nanao, it's because they weren't allowed together.

Also, reading between the lines here, but are Katen and Shunsui the parents of Nanao, and by extension, Kyokotsu, hence why Shunsui could use it? That would make Nanao a Zanpakuto/Shinigami Hybrid. Damn, that'd be interesting.