After firing Mugetsu Ichigo's power gradually fades. His transformation also unravels.
Aizen is collapsed after the Mugetsu. He's not dead due to his regenerative abilities, but his transformation is also unraveling.
Ichigo lands down at Aizen's location. He kneels as his shinigami powers vanish.
Aizen stands completely still before him. "This is your defeat," Aizen says as he shows his sword.
Aizen's sword vanishes. Aizen says the hougyoku has judged that his sword is unncessary. Because Ichigo has lost his power the difference in their powers is even greater.
But just as he says that light rays pierce Aizen's chest. "What is this?" he asks. "I've finally invoked it," answers a voice. It's Urahara.
He's talking about the kido he tried before Aizen completed his transformation. Because Aizen can't be killed when fused with the hougyoku he's decided to develop a new technique to seal him.
Aizen says to Urahara that it's too bad. "Since I've evolved further that level of kido won't be able to seal me!
However, just as he says this Aizen's transformation unravels even further, and even his face is like that of his shinigami form. Aizen is shocked as he senses his power fading.
"That's the hougyoku's intent. As your power has weakened it doesn't recognize you as its master," says Urahara.
"That's impossible!" screams Aizen at Urahara as he starts getting sealed. "Why would someone as intelligent as yourself follow someone like that!"
"Because I observed the Spirit King. If the Spirit King didn't exist Soul Society would break apart. The Spirit King is the lynchpin, and is he is lost it would easily crumble. That's how the world is," replies Urahara.
"That's a loser's theory! A winner should never wonder what the world is like but rather how it should be. I am...!" As Aizen is cutoff Ichigo averts his eyes.
The next page is Aizen being sealed.