User blog comment:Xilinoc/Ch. 683 - The Dark Side of Two World Ends/@comment-3430033-20160721141457

An interesting observation:

"I figured an explanation of what happened is in order: First, Aizen makes himself appear as Renji and uses his Bankai. Then, after losing his arm, he makes him appear like his original self, and casts Goryuu Tenmetsu. Then, after being blown away, he makes himself appear like Ichigo, but cleverly makes it seem as though Renji from earlier was actually Ichigo, and puts in a few flaws to make that clear to Yhwach (you can see parts of Souou Zabimaru falling off Ichigo, as well as his arm being missing). Finally, Aizen removes all illusions to show that it was him all along. Renji isn't in this chapter at all, and Ichigo isn't in it until the second last page. Before that, it's just Aizen using illusions to make himself appear as the other two."

Credits to Andygoesrawr on Bleach Reddit.