"You've certainly come along in your studies, Twilight," Celestia said as she looked over her student's latest report.
"Thank you, your Highness. It's only because I have such a good teacher."
"Well, as your teacher," Celestia stood and paced around the much smaller unicorn, "I think it's time to try something new. Or rather, it's time to retry something."
"I'm sure you remember your first, hmm, encounter with real magical power?"
"Oh... yes." Twilight hung her head. She knew where this was going. "Princess, I don't think I'm ready. I'm not sure I'll ever be-"
"And I certainly don't expect you to be." Celestia nuzzled Twilight on her cheek. "This is merely to see how far you've progressed. I'll be with you the entire time." Her voice dropped to a whisper, as a mother might use towards their child. "I won't let anything bad happen." Twilight looked up at her. She bit her lip, but after a moment, nodded weakly.
Celestia guided her student to the center of the circular study, as far away from its high, heavily adorned walls. She Twilight stood directly in the middle, Celestia facing her. The unicorn tensed as she felt magic, Celestia's very own, reach around hers, nudging it, poking it. Her mentor's magic was always warm, always inviting, but to have even less control made Twilight uneasy.
As Celestia found the lock in Twilight's mind, the unicorn panicked. She tried to shout, to tell her to stop, but she was drowning. Everything was a blinding white. As she searched for her voice, any sound to tell her mentor of the pain, her discomfort eased. Colors she had never imagined bled into the endless brightness. Where had this been before? Had she not been strong enough to make any sense of the cascading energy when she had earned her cutie mark? She craned her neck up to see as much as she could. Flitting in and out of the storm, like fish in a rapid, magic the color of fire guided her own energies.
A soft cheek pressed against Twilight's, and through it all she could hear Celestia ask her, "What do you see?"
Alternate response: "My god, it's full of stars!"
Aaaand that's as much fanfiction as I'm going to get into. It actually turned out longer than I expected. As much fun as it is to poke fun at Trollestia and everything, I think Our Little Sun Goddess is a lot better than we give her credit for. Princess or not, the fact that Twilight trusts her so completely implies a powerfully positive relationship.
Done in PS CS4