Here you are, Ellie, the little happy piece I said I'd do. :P It's a sort of 'happy ending' if you will to an otherwise tragic scene.
"I can't kill my brother."
And he hadn't lied. He truly hadn't, he'd always known that no matter what happened, he could not kill Lucifer. It wasn't that he was a coward or that he was afraid, it was that he physically could not kill Lucifer. Lucifer was the best brother he ever had, in saying that, he's got so many brothers and yet, in all the time separated from them, Lucifer remains the one he misses the most. Lucifer had taught him all he knew, in essence, Gabriel was just Lucifer in training and this time around, the Apprentice doesn't kill the Master, the Master doesn't kill his favourite student either, he just makes it look like he did and that's good enough for the both of them. It's the most meaningful 'goodbye' they can ever hope to receive. The most heartfelt 'I love you, bro' either of them could ever hope to get. The kindest end to a chapter of broken dreams, bloodshed and fallen angels.
