For it to be that easy for this illusion to subsume his Amaterasu could only mean -- but no, it could only mean that if this were real. In a genjutsu, the laws of reality were dictated by shinobi who controlled the senses. His chakra was ensnared in the very fabric of illusion right now; it would be child's play to remove Amaterasu, and of all people Madara would know what it looked like --

What it felt like -- because the alternative was not one that was possible.

What it meant was that Mangekyou-based techniques were all fair game for manipulation, the gift of his brother's eyes too familiar to the men who had ensnared him. Even as the last dregs of the arrow nicked Itachi's shoulder (a strange reversal, and all realism --), Sasuke dropped Susano'o, the pain of maintaining it vanishing into bone-deep ache, and blurred towards the image of his past, hands spinning through seals for fire manipulation.