User blog comment:Xilinoc/Ch. 541 - THE BLADE AND ME 2/@comment-3230060-20130613145316/@comment-6943043-20130614195151

for the second and third parts, i think that when (fake) zangetsu uses bankai, i think that zanpakuto spirits have full control over the blade's powers, which explains how easily they decimated seireitei when muramasa "freed" them. that may be why he becomes so young and handsome, because shinigami only can use at least a fraction of their zanpakuto, even if they use their true power. also, when ichi used FGT, his shinigami powers (h/ichigo) were lost but his quincy powers ((fake) zangetsu) were already present, they hadn't yet "awakened".

this is however, JUST A THEORY.