Aizen's and Ichigo's battle in Karakura Town ended in a catastrophic defeat for Aizen. With Ichigo's final attack, Aizen was absorbed within the veil of darkness of Mugetsu. Having his reality torn apart before awakening within a world of absolute filth, his world of Soul Reapers and Hollows is merely that of the past as this new world has paved a new foundation of mystery for him.
Madara Uchiha's shock when Black Zetsu who was his most trusted ally betrayed him brought confusion and hatred. Unable to continue on, he eventually lost his strength as he dropped dead. Passing on to the afterlife, he was confronted by the Sage of the Six Paths who offered him a chance that led him to be reborn. Bringing him to a whole new world for the Legendary Uchiha.