Twilight Sparkle tried not to be an angry pony. Oh, sure, she had her outbursts. Maybe one Pinkie Moment too many. Maybe a burnt book, or a ‘friendship problem’, or even ponies disregarding her concerns about tar... never mind. She really did try her best to avoid getting mad. But when she finally looked closely at the dress Rarity gave her for the weekend, she had a sudden flash of just how angry she could get. A sort of hypothetical anger zenith, some pure paragon of flaming rage. Well, let’s be more accurate. What made her angry was just how little dress there was.

“I can not BELIEVE the nerve of that mare!”

“Twilight...”

“Does she really want me to wear this to a royal function?”

“Twilight...”

“She expects me to squeeze into this thing like some kind of two-bit red-light hitching-post whors-”

“TWILIGHT SPARKLE!”

She immediately went flat to the ground, knees bent, hindquarters in the air, head bowed as low as physically possible. It was half-instinct, half-reflex, and entirely unconscious.
“ohno I’m sorry I didn’t...”

Celestia looked at her with... Well, Twilight had no idea. She couldn’t see Celestia, what with her head being so low. But regardless, I am sure Celestia looked on her with some emotion.
“Twilight. Calm down. It’s perfectly fine to be a bit upset at the surprise, but that may have been an over-reaction..”

“But I’m... I’m going with you. I can’t make you look bad. I’d feel horrible.”

“If anything, Twilight, you will be doing quite the opposite. I’ve seen far more risque fashions in my court before, and on mares and colts younger than you, for that matter.”

Twilight rose, slowly, not quite sure what to say. Celestia was looking at her with concern, genuine and warm, and just like that, she managed to relax, the tension leaving her in a single gust.
“...Alright. I suppose I’ve just been bottling up my reactions lately, and I probably... Overdid it a bit.”

Celestia smiled.
“We all have our little moments. Self-control can be quite taxing- Even with centuries of practice.”

They shared a laugh over that one, and Twilight managed to calm down, bit by bit. She was still wary, of course, but she was no longer mad. That didn’t change the fact that a certain fashion-pony was going to be hearing a lot of angry ranting Twilight. All of the angry ranting Twilight, in fact: The whole bundle. But that could wait. First, it seemed like she had to survive a date. A first date. A first date with her marefriend. A first date with her marefriend who is also her ruler and the pony responsible for THE SUN ITSELF.

Maybe nervousness is better than anger, now that she thought about it. Abject terror is acceptable as well.

--------

Strangely enough, Twilight had never actually seen the Royal Baths before-- She had her own rather nice accommodations in the observatory, and never had any reason to use those at the castle. But seeing them now, she regretted that fact. It was...

Celestia stepped up the stairs next to her.
“Beautiful, isn’t it?”

Words had, for a moment, left her.
“Mmhmm.”

A chamber some hundred or more feet on every side, enclosed in a dome of pure crystalline glass without a single seam or rivet. There was no way to see inside, of course- Between the smokey tinting of the glass and the defensive spells on the castle as a whole. But the result was a bathing chamber from which one could see the entire Everfree Forest, much of Ponyville, and a fair chunk of the surrounding countryside. The actual baths themselves were equally preposterous, in both quality and scale. Four individual pools, each large enough to contain a dozen ponies or more, surrounded with faucets and baskets and towels. A single small door on the far wall allowed attendants to come and go without issue, and the bathers themselves entered from below, coming up from a massive staircase that exited on the dry tiles at the center of all four baths.

“Are we... Are we going to be alone, here?”

Celestia chuckled and nodded, stepping forward and nudging Twilight towards one of the baths.
“I do believe so. What that means is entirely up to you, of course.”

She blushed and dipped one hoof into the water, finding it perfect- Deliciously warm, perhaps just a little too hot, but that was how she liked it. Although with the way Celestia was speaking, and how close she stood, a very brisk cold bath might have been more... helpful. As she descended into the water, the difference in size between Celestia and herself grew more apparent. With every step, it seemed like she went from being half the princess’ size to a bit smaller, and a bit more... By the time her mane hit the water she felt absolutely minuscule, completely dwarfed by the heat of the baths and the sheer presence at her back. And if that made her want to plunge into the water face-first and stick her hind legs in the air, presenting herself to the alicorn... Well, her self-control stood the test. Barely.

Celestia followed her in, eventually coming to rest just next to her, sliding onto one of the stone benches within the water. A flurry of telekinesis, too quick for her to see, and a dozen different oils, fragrances, and flakes hit the water, suddenly filling her nose with scents of spring and nature and... She breathed deep and sighed. It was going to be absolutely painful to go back to Ponyville and her simple tub... But then again, now she didn’t have to actually consider getting mad at Rarity. She could just tell her about these baths, and watch the look on her face when she realized she may not ever get the chance to use them. That would be payback enough, most definitely.

But that could wait- For now, she relaxed and reached over to grab a scrubbing loofa with her magic... only to have it snatched from her grasp.
“Ah-ah-ah! As my guest, it is my duty, and pleasure, to take care of that for you.”

“But Princess, I-!”

“What did I say about titles?”

“Mmmh... Alright, Celestia. Thank you, in that case. It’s an honor.”

“The pleasure is all mine.”

As revered and holy as Celestia was, Twilight wanted to call that a lie. Because after a minute or two under the gentle ministrations of a half-dozen scrub brushes, loofas, and combs, Twilight had enough ‘pleasure’ to last her weeks. Even though it was just an entirely normal bath, nothing sexual involved, she found herself panting from time to time, her tail lifting to the side out of reflex. She was almost more disheveled than when she started, or so she felt-- Her legs were straining in the water, trying to rut against a presence that wasn’t there. It felt terribly dirty, and at the same time right. Celestia, for her part, was simply humming and happily working on her student’s mane.

Twilight decided to ignore her traitorous body’s heated twinges, and began to hum along with the Princess. It was a fairly simple piece, repetitive in a sort of looping, wavy way. It was certainly the kind of tune that got stuck in your head easily, and... Mmmh. She almost lost the beat when the heat between her hind legs got even stronger. Celestia was focusing on her tune, moving up an octave to match Twilight, which was good-- Twilight was sure that if her mentor looked down, she would have something to say about it. But now, she didn’t know if it would be something encouraging... And how she would react if it was.

The bath continued for a bit longer until she finally, begrudgingly, came to a resolution. It felt wrong, but she couldn’t deny what she was feeling. Her senses came to a single conclusion.
“You’re doing that on purpose, aren’t you?”

Celestia broke out of her song... And confirming Twilight’s suspicions, the rushed heat of her ‘agitation’ began to abate immediately.
“I’m sorry?”

“I almost didn’t notice it at first, but... I’ve been feeling strange ever since we got in... Or, more accurately, since you started humming. And I think you might have been doing it on purpose.”

Surprising her, Celestia responded with a broad grin, leaning down to kiss Twilight’s forehead.
“Very good catch, my prize pupil- I will admit, I was tempted to be more obvious. But I can assure you not all of that was my doing.”

Twilight couldn’t help but agree-- Certainly the sense of direct stimulation were gone, but her feelings towards her mentor weren’t exactly anything new or recent. She’d been feeling rather ‘eager’ ever since they woke up that morning.
“...And I can assure you I didn’t mind in the slightest.”

Celestia stared for a second before breaking into laughter.
“Aaaah, Twilight. I... I’m truly glad you wrote me that letter. This seems like the beginning of something I’ve been looking for- Somepony who can actually keep up with me... In all regards.”

At first, she took that statement literally, and blushed. But then she thought back to the bath itself...
“Wait, do you mean that I was doing that to you as wel-”

Celestia nodded, a faint blush of her own appearing- Twilight had never seen the Princess express herself like that, and found it to be one of the loveliest sights she had ever been treated to.
“And quite well, given that you did it accidentally. I’ll have to teach you that more directly sometime soon... Along with some other things.”
She winked, and Twilight ducked her head under the water, glubbing out an inaudible reply.

--------

Something was tugging at Twilight. Well, alright, there was a brush going through her coat. That was certainly part of it. But something was pulling at the back of her head. Alright, yeah, there was the comb in her mane. Again, not the actual issue here. There was a thought nagging her...

“Celestia?”

The Princess paused in her multi-tasking of brushing, combing, and handling a second comb at Twilight’s tail- She had insisted, saying she missed doing this kind of work for somepony else.
“Yes?”

“You said that when I hummed that tune earlier, it, um... affected you.”

“That it did.”

She scrunched up her face in confusion, trying not to sound as baffled as she was.
“How? I thought magic required focus and intent, that it was always conscious. But I was just humming that tune- I wasn’t focusing on anything, and I had no special intent.”

“Well, those aren’t mutually exclusive facts.”

Neither one of them spoke for a while. Celestia often posed riddles like that one in their studies- Twilight would ask a question and lay out the facts as she understood them, Celestia would point out an error, and allow Twilight to logically deduce the truth. She had missed this old practice, and trying to resume it with Spike and her various friends in Ponyville had been a total strike-out. And while this one took her longer than most (nearly a minute and change) she came to a conclusion.

“But I was focusing on the tune, and I had some amount of intention, or at least idle thoughts, in regards to... those feelings. So that means... the song itself is magic. Thus, by consciously singing it, I was casting a spell?”

Her mentor took that opportunity to lean down and kiss her, leaving her dazed for a moment.
“Very good, Twilight! It’s not terribly common, nor something all unicorns can do, but there are spells that come in such forms- Poems, tunes, moving in certain ways, that sort of thing. Luna and I often find them to be very practical, and we enjoy discovering and using them quite a bit.”

“But... my special talent isn’t with any of those things. I’m not a singer or a poet or a... I don’t know what a special talent for the third one would be.”

Celestia ran the comb through a particularly troubled tangle of tail, pausing to rub her cheek against Twilight’s when she heard the wince that resulted. Twilight, for her part, blushed hotter than she already was from the kiss.
“Mmh. A martial artist, or a sculptor. An athlete? I suppose anything like that, really. But not only are you entirely capable of it, you have two reasons for it.”

“My special talent being magic itself... and the Element.”

“Yes, to both. You’re a very gifted unicorn, Twilight. And a very thorough one, I might add- Some great talents, like Starswirl the Bearded, were quite broad-based. Others, such as Silver Gaze, were specialists. You could choose to go either way, or even walk a middle path.”

“I... Am I really that great?”

The combs and the brush stopped, and Celestia stepped forward to look at her. Her eyes were arresting, their bright magenta softened by the room’s light. Twilight wanted to back up, or move forward, and could not make the decision, so she just looked into her marefriend’s eyes.
“Twilight... I chose you. For many reasons- And that is one of them.”

“Celestia?”

“Yes?”

“...May I kiss you?”

“You don’t have to ask.”

They took their time getting ready at that point. No sense in rushing, after all.