User blog comment:Xilinoc/Ch. 568. Hear. Fear. Here 2/@comment-5693502-20140212122816/@comment-26420452-20140212163823

I too think the Byakuya's Zanpakutō is complete in the sense it cannot get an ulterior form. However, his Bankai has different variations (Senkei, Gōkei, Shūkei) so I guess he has learned a new variation of it.

And I empathize with you over the Fear - Sode no Shirayuki explanation.