Aizen is perceived as the master orchestrator behind everything in Bleach, and this theory explains how that might be true.

He did so to create an army of Arrancar in Hueco Mundo to attack the Karakura town ... his fight against Ichigo as he was seen shouting at the former Squad 12 captain. Sosuke Aizen as seen during ...

As the archetypal Bleach villain, Aizen is much like Frieza ... The intent of unleashing this Hollow on Karakura Town was to cause some sort of mutation to fight Soul Reapers.