Bleach fans need to trust in Aizen and re-read the chapter where Askin defeats Ichigo because there's an obvious explanation ...

Aizen’s absolute control over his reiatsu, and why Ichigo’s lack of mastery prevents him from passively destroying weaker beings in Bleach.

Shunsui makes a deal with Aizen to aid Gotei 13 in the battle ... monstrous transformation. He's hit by Ichigo's Final ...