"Doctor."
The Twelfth Doctor turned around from where he had been examining the console, his train of thought broken as he saw his younger self from three incarnations ago. The Ninth was leaning against the the railing surrounding the console, his arms crossed.
"How did you get in here?"
"It's the TARDIS. I have the key."
"Right…"
"We need to talk."
"What is it?"
The Ninth's face was a mask, something the older Doctor remembered as an expression hiding deep dislike. He did not speak.
"Oh, I know, you don't like the look. Times change. Sorry."
"I heard that Gallifrey is safe."
"Oh no, no, wait, hang on. You're not supposed to know that-"
"Did you do it?"
"Well, yes, I did. We did. My past self and two others."
"Why?"
"For the greater good."
The Ninth blinked.
"For the children. Do you know how many were going to die that day?"
"2.47 billion children did die that day."
"No, we saved-"
"They died. Have you got that? They had to die because they already did."
"But children are… Children are valuable-"
"Don't talk to me about their value! I knew their value. They were in a place where death would have been kinder then the hell they were going through."
"Look. What we did, it was for the greater good. It was a fulfillment of the Promise I made."
"What I did was. What you did was not. I saved the universe by giving the Time Lords the best ending I could. You've endangered the universe by saving their lives. Going back on a choice like that is breaking the Laws of Time. Gallifrey's destruction is a fixed point."
"Sometimes the rules need to be bent."
The Ninth walked over to his future self. "Look, I'm still recovering from what I did, and now, in my future, I'm expected to act like the worst part of the Time War never happened? You say you've made my life better, but you know what? You've made it a sham. I'll forget this conversation as soon as I leave here, and mourn my loss, while you're standing here, knowing that what I did doesn't matter in the end, because you fixed it."
"I couldn't let them die," the Twelfth murmured. "They didn't deserve it."
"One word: Adric."
The Twelfth stared at him. "Don't you dare think you can pull that one on me!" he said in a low voice.
"Why not?" the Ninth replied sharply. "By your logic, I should go back and save him. I should leave my - our - Fifth self to die regretting that he couldn't save him, while he's off adventuring with me. It wouldn't be fair to my earlier self, but at least he'd be alive."
"That was different!"
"Sure it was. I wasn't a stupid ape back then."
"When you get to be me, you'll understand why!"
"Even when I do, I'm sure there will be others that won't. The universe is watching us. We can't muck about like we're the messiahs of space and time. That's not the role of the Doctor."
The Twelfth turned away, and walked over to the railing. "This is pointless. I can't help you understand. Just go."
The Ninth turned and walked towards the doors without another word. The Twelfth put both hands on the railing and let out a long, sad sigh as the doors closed behind him, leaving him in the cold light of the TARDIS.
AN: I know this story comes after the Twelfth's regeneration, but I am not writing this to say I hate the Twelfth. While he's not my favorite Doctor (that would be a tie between Five and Seven), I felt like I could capture this argument better with him since his speech patterns are freshest in my mind. Once I have the chance I may rewrite this with Eleven, but since Twelve has lived through that choice of not destroying Gallifrey for a while, and since he was the one who ended up making the decision of breaking another fixed point by saving Clara, it's clear, in my opinion, that he does not have as much regard for the Laws of Time as much as he used to.
I would request that if you disagree with me on my opinion on the fixing of the Time War, that you at least tell me why. If you agree with me, let me know.
Thanks for reading, and cheers to the Thirteenth Doctor!