It is necesary to state the fact that, since over 100 years ago, Aizen was planning his treason to Soul Society; in order to accomplish this goal, Aizen, among his numerous heinous acts, conducted several hollowfication experiments in order to create the "ultimate Arrancar", and sadly for Hirako and the other to-be Visored, they were his main focus on the Hollowfication Incident, not to mention Urahara's framing and subsequent him and the Visored's exile from Soul Society.