A moment earlier.
Just when Rex was about to help the others, his eyes widened as a voice entered his ears.
There was no mistaking the voice—it was Evelyn's, and Rex knew it instantly.
Gazing downward, he could see a string of Luna energy attaching to his chest.
It was the string that allowed her to communicate through the madness of the battlefield.
"Leave us," the voice rang inside his head, surprising him completely. "Focus on the Executor, focus on your fight with him. Make sure that you'll win. Leave us—we can handle this spell by ourselves!"
Naturally, Rex wasn't going to listen to Evelyn.
Compared to the risk of them being wiped out, there's no way that Rex would leave them.
He had resolved to confront the Executor alone so that the others would be safe, so the idea of leaving them to face an attack powerful enough to nearly vanquish him was unacceptable, Rex was not going to let that happen.