Castiel sighed, like the weight of the world was on his shoulders. He'd always had a bit of a too-serious, hangdog look about him, but he was particularly bothered about this.
"I ... may have led the charge against Raphael," he said, glancing up again.
Angelic civil war. Angels followed orders, they didn't question them. An archangel's word was law, and Castiel rebelled.
He'd been trouble since he touched Dean Winchester. He'd been trouble before that, when Castiel was created different from the others, broken — prone to questioning orders, prone to overthinking. He'd needed to be fixed, his mind wiped and reprogrammed and reconditioned. He needed repairs, and the angels like Naomi had been kind enough to fix him rather than simply kill him for being impossible to deal with.
That, from an angelic standpoint, had been quite the mistake.
"There was war in Heaven," Castiel explained. "Brother turned on brother, everyone scrambling for more and more power in order to gain the advantage."