So, I actually didn't write this. My little sister did. She thought of this while watching Flatline. I only touched up on some minor things. So, congratulations to my sister on her first fic!
"Go make sure everyone gets in the TARDIS, Clara." The Doctor said. He'd just defeated some new creatures that he dubbed the Boneless. Everyone was safe again.
As the Doctor was walking back to his ship, something caught his eye. There was graffiti all over the walls of the tunnel, but there was one that was unique. It had been centuries ago, millennia. Two words scattered across time and space. A message that saved his life.
Bad Wolf.
The Doctor held his breath. Even now they were strewn through his timeline. He'd promised himself long ago that he would never forget those words. Because those words meant something more precious than life. They were traces of a person lost to this world.
As he gazed at them, he reminisced. Her blonde hair and hazel eyes. She had been everything. But now it was pain and regret. However much he disliked the feeling, he didn't want to lose that pain. No pain meant that it never happened. And he wouldn't trade the multiverse for his time with her.
He let out his breath in a sigh and walked the rest of the way back to the TARDIS. He needed to get those people home.