Board Thread:Questions and Answers/@comment-28648393-20160604120905/@comment-1970092-20160604164014

Essentially, after Ichigo reforged his Zanpakuto Zangetsu, Ichigo learned to combined his Shinigami/Hollow and Quincy powers to create this form. However, by his own admission, he hasn't mastered this ability yet, and as such, needed to use Yhwach's Quincy Reiatsu to wake up Zangetsu (the Shinigami/Hollow spirit), which was represented by the larger blade turning white. In this form, Ichigo could use Gran Rey Cero combined with a Getsuga Tensho~