Aizen is quite challenging to manage as just energy is not adequate to defeat him. Though Aizen has enormous toughness and spiritual power, He rarely takes advantage of it.2nd Fusion (?2???, Daini no Y?g?): Just after Kisuke Urahara tries to block the Reiatsu vents in Aizen's wrists having a seal, Aizen emerges with the ensuing explosion unscathed