Board Thread:Questions and Answers/@comment-10797017-20130622101437/@comment-5657895-20130626222411

I suppose a Zanpaktou in general is supposed to be forged with a single spirit, intwined with the individual wielding it. Having a dual manifestation implies that those individuals have twin spirits or some kind of split/dual reitsu or spiritual characteristics, which is special in it's own way. Just my theory on why.