"Don't!" As Luna advanced, Twilight backed away, maintaining the distance between them. Mist curled around the light of their horns, concealing the world, and hiding them from all but one another.
"Twilight, please! I—"
"Don't you dare say it," Twilight sobbed. Tears ran freely down her face, yet she refused to look away. Even in her pain, Luna could feel a welling of pride at the strength Twilight displayed.
"I—"
"You monster, I said don't you dare!"
A wave of raw, undirected magic buffeted Luna as it passed by. For a moment the mist roiled and fell back against an expanding sphere of energy, but the magic's power was quickly spent, and soon the inky grey wall had closed in on them again.
Now Twilight finally looked away, closing her eyes in a show of finality that was unmistakable. She sniffed, and choked, and Luna was overcome by the urge to rush to Twilight's side. Yet she held back.
"I had begged you would not be forced to make this choice. I prayed... to whom did I pray? Myself? Celestia?" Luna lowered her head. "I thought you were dead. I thought—I thought I was alone, Twilight."