User blog comment:Xilinoc/Ch. 651 - The Theatre Suicide SCENE 5/@comment-2120712-20151112092950

My understanding of Nanao's zan and story:


 * Oetsu gave the then Ise Family patriarch their zanpakuto. The Shikai name of this blade was Kyokotsu. The family not wanting to dull their Kido abilities decided to pass their only zanpaukto down the family line(and reject the taking of other zan) BUT the unfortunately consequence of this was a curse that killed off male members of the family.


 * Nanao's mother wanted to escape this curse. She thought by breaking ties with her family and marrying into another(I presume before this that men that marry an Ise change their family name to Ise) family. She marries Shunsui's older brother but he dies to the curse as well, but they consummated their marriage beforehand and she was pregnant with Nanao.


 * She returns to the Ise family gives birth to Nanao and later confronts Shunsui and tells him her family history and curse. Using Katen, Shunsui creates Okyo that seals away Kyokotsu. However the result was that part of Kyokotsu powers merged with Katen and created a new Kyokotsu, one that while in Shunsui possession did not kill him but maybe where the aspect of it being able to kill Shunsui if he loses the games Katen comes up with comes from.


 * Nanao's mother told her the basics of what's going on in hope that Nanao would be able to break the curse for good as the current "seal" is based off of I assume Shunsui being alive which is bad due to his line of work.


 * Nanao goes through the Shinigami Academy and probably was scouted to the Kido Corps but was pulled into the 8th Division by Shunsui's influence(speculation on my part). There she moved up the ranks due to her excellent Kido skills that were good enough for her to be LT level without a shikai.


 * Nanao takes up the cursed Kyōkotsu and it either merges with her Zan to create Hakyoken, or she imprints upon Kyōkotsu and Hakyoken is born.


 * Its power does not allow it to kill humans but it can perhaps kill off shoots like Hollows and Quincy but not Shinigami or regular humans. Its power may have accumulated over time being that it could of absorbed the powers/potential zan spirits of successive Ise holders + Shunsui's Katen).