User blog comment:Xilinoc/Ch. 651 - The Theatre Suicide SCENE 5/@comment-1210805-20151112072840

I'm still a little confused about this one. From what I can gather, Nanao might not actually be related to Shunsui. His brother married Nanao's mother when he was quite young and at some point he died, Nanao's mother was returned to the Ise family and entrusted the sword to Shunsui. Now, the obvious conclusion to draw from this is that Nanao is Shunsui's niece, but if her mother had her after Shunsui's brother's death then she might not be related at all.