Poof!
Celestia barely looked up in time to snatch the letter before it fell into the steaming water around her.
"What is it now?" The irritation in Luna's voice was evident as she moved from her suddenly shifting sister's side and leaned back against the rim of the hot spring. "We are on vacation, 'Tia!"
"A letter from Twilight." Celestia broke the seal with a flick of her magic. "You know as well as I she would never interrupt our getaway if it wasn't important."
"Mmmmrgh. Read it and be done with it." Luna laid her head back and closed her eyes irritably.
Dear Princess Celestia,
I realize it's been a while since I sent you one of these, and thought it might be nice. For old time's sake.
This week, I learned ruling is hard. Ponies expect so much, and there's only so much I can do. I knew it before from my royal duties, but doing everything all by myself? I don't know how you did everything alone for so long.
Or maybe I do, now. It's important for a ruler to have ponies (and dragons -Spike) Yes, Spike, and dragons—who can help you when you need it. Whether it's with an unusual point of view, an unconventional solution to a problem, or just a friendly shoulder to snuggle up to when you're stressed, no ruler really reigns alone.
-Your faithful student friend, Sorry, habit. -Spike
Twilight SparkleP. S. Humans are warm!
Celestia's laughter echoed off the rock walls around the hot spring, causing Luna to open her eyes and raise an eyebrow. "Something is amusing, sister?"
"Twilight has met my 'snuggle buddy.'" Celestia glanced at Luna.
"The ape-creature from another dimension?" Luna snorted dismissively.
"The human, yes. Apparently, he's been very helpful to her."
"So all is well in Canterlot?" Luna approached her sister, eyes intent.
"Better than I hoped or expected, it seems."
"And we don't need to return and rain sunfire and moonrocks on some invading demon from Tartarus?" Luna was nearly touching Celestia.
"No."
"Then we start over." Luna snuggled up against Celestia again and smirked contentedly.
"Start over?"
"You promised me a solid week of sisterly bonding time, with no interruptions. Six days, eight hours, twelve minutes, and five seconds without word from Canterlot is not a week."
"But—"
"Nope. Snuggle time now." Luna pulled Celestia down against the rim of the hot spring like an oversized teddy bear.
"Very well, then. A promise is a promise, after all." Celestia grinned and snuggled closer, herself. "I hope Twilight doesn't worry too much when we don't return in the morning."
"She's smart. She'll figure it out." Luna flipped the nearly-doused letter away from the spring with her magic. "My Children will tell her, if she doesn't." Exactly as promised. Well done, Twilight.
Celestia sighed contentedly. "And hot springs are warm, too."