Board Thread:Questions and Answers/@comment-27392440-20160221191403/@comment-44061-20160222042122

its stated to be a zanpakuto for one and for two the thing that makes it unique is that its a not individualized but it is passed down with only the head of the Ise family being able to use it. So apparently because of the nature of the family and the swords status as a religious relic its use and position are simply unique. No its nothing like ichigo, he just never had an asauchi to imprint on, the fact that originally the hollow-like creature that infected his mother was based on a similar composition as an asauchi allowed him to form a sword without a actual asauchi. Thus he had a faux zanpakuto. Nanao couldnt imprint on a asauchi even when she tried because of the nature of her family and their connection to the holy relic. She never used a zanpakuto cause she never had access to one.