Complex sentence: Aizen then almost reveals Ichigo's lineage when Isshin intervened to take over the fight prior to Aizen revealing that he absorbed the Hōgyoku as it grants his desire for a Hollowfication-like form to easily defeat his enemies.
Split into simpler sentences: Aizen then almost reveals Ichigo's lineage when Isshin intervened to take over the fight. Aizen reveals that he absorbed the Hōgyoku as it grants his desire for a Hollow-like form to easily defeat his enemies.