"What the hay?!"
Trixie's entire wagon shook violently from the force of a nearby explosion, throwing her out of her hammock. She remained on the ground for a few seconds, silently cursing herself for thinking parking her wagon under Twilight's castle was a good idea. Then again, the privacy and reliable shade were always quite worth it.
She quickly clambered back on her hooves and brushed herself off, giving a brief look of annoyance on the newfound mess on her wagon floor. After magically reorganizing any fallen trinkets, Trixie bucked open the doors to her wagon and trotted outside to look for the pony she would exact revenge upon for the loss of a good nap. What she was not expecting to see, however, was a large cloud of smoke billowing out of Twilight's castle. Specifically, out of Starlight's window.
Hmm... that's not good. Umm what do I do what do I do what do I do... Knowing how powerful of a unicorn her friend was, Trixie was certain that Starlight was more than capable of taking care of whatever shenanigans Ponyville had to offer. However, there was still that feeling lingering in the back of her mind that she should at least check to make sure her friend was alright.
Ho humm, might as well go help. Celestia knows where she'd be without me now. She rolled her eyes and grinned as she levitated her signature cloak and hat off their stand onto her body. She stepped off the wagon and gave a quick wave of her horn, splashing a camouflage spell over her wagon to ensure no peering ponies let curiosity get the better of them. Once she was satisfied, she trotted towards to the front door of the castle.
Okay Starlight, just a few more layers...This time it'll work... The lilac unicorn gritted her teeth as she poured more magic energy into her horn. The glow around it was almost blinding, casting her surroundings in a bright, teal hue. Pure threads of magic spilled from her horn, swirling around her like a mystical whirlwind.
Come on you, stay together... Starlight gritted her teeth to ward off the rising headache and furrowed her brows in concentration. Beads of sweat trickled down her forehead, and she panted for breath. Slowly but surely, the magical strings began to stitch together in front of her, forming a giant sigil of arcane energy that spanned the length of her room. Her eyes widened.
Yes yes yes yes yes! This could be it. The key to the door. The last piece of the puzzle. The answer sheet hidden upside down on the back of the test. All she needed to do now was activa-
CRACK!
Starlight's ears twitched at what was considered the worst sound a spell caster could hear. It was the magical equivalent of the sound of bits tumbling down a drainage grate. In her case, it was the sound of a magical tear ripping through the fabric of her spell.
Something's wrong... Starlight peeked an eye open and, to her horror, noticed a large, glowing crack slowly growing along the middle of the spell circle. She double checked her algorithm and quickly realized something extremely important was missing. Something big. Something obvious. Something just beyond her reach. And without it, her spell was rapidly falling apart. More cracks splintered off the first, quickly running across the flickering sigil of light.
Starlight's eyes widened in panic. No no no no no! Please, not when I'm so close! She pleaded with the spell to stay together, offering more of her magic in an attempt to stabilize the broken sections. The glow around her horn doubled, then tripled in brightness. At first, it appeared her efforts would be in vain; the cracks continued to grow until they almost covered the entirety of the spell. However, the spread of the cracks gradually began to slow, and a flicker of hope crossed the unicorn's straining mind.
She inhaled sharply, filling her lungs with more precious oxygen, and gritted her teeth as she poured all her energy into maintaining the unstable regions of her spell. Her head was beginning to ache from the strain, but she paid it no attention. For a minute, it seemed she and the cracks were at an impasse, like two ponies in an even game of tug of war. Soon, she noticed the cracks beginning to recede, slowly but surely. Her eyes lit up with a newfound fire as her magic raced along the glowing tracks, mending them and chasing them back to their origin. The original crack was now no longer than her foreleg. Just a little bit further and-
BANG! "Starlight! The Great And Powerful Tri-"
Starlight's focus completely collapsed from the momentary distraction. Her magic cut off for just a split second out of surprise, but that small slip up gave the cracks the ground they needed to overcome her defenses. In mere seconds, the cracks spread out through the entirety of her spell, giving the appearance of a bright, pulsating spiderweb. Starlight realized her spell was beyond any hope of recovery and, after only a moment's decision, abandoned it altogether. She dived towards the only other living pony in the room and instinctively cast a crystal shield spell around them both as the room was bathed in a blinding white light.
Starli- ... are yo- ... -ight...
A voice rang out faintly in Starlight's head, shifting in and out of focus like watching a distant searchlight through a thick fog. She concentrated her will on it, trying to bring the sound into focus.
Wake- ... -me, Trixie... WAKE UP!
Two recognizable words cut straight through the fog clouding her mind. She focused on them and obeyed their command, dispelling the fog just enough to be able to peak open her eyes.
A pair of wide, grayish violet eyes stared back at her from less than a hoof length away.
"AH!"
Starlight's shout elicited a surprised "Eeep!" from the pony occupying her personal space, who jumped back just enough for her to briefly take in her surroundings. Her floor and walls were covered in scorch lines, and some of her furniture had been knocked over. One of her bookshelves appeared in immediate danger of toppling over. The protection spells on all her precious kites remained intact however, as she noted with satisfaction that none of them had a single mark of damage.
She turned her attention back to the pony in front of her and did a quick once-over. Lilac blue fur, magician's cloak. She only knew one pony who fit that description.
"Trixie?! What- oh my gosh, are you okay? Why are y-... wait, you... YOU! You're the one who interrupted my spell!"
Trixie's eyes widened in surprise. "That was your spell?! Trixie thought you were in some imminent, magical danger!"
Starlight let out a dry laugh. "When it comes to me Trixie, I don't think those two are entirely mutually exclusive."
Trixie cocked her head.
Starlight rolled her eyes. "Meaning both can be true."
"Psssst, hey Starlight." Trixie leaned in towards Starlight's ear. "You know you can speak Ponish when it's just the two of us. You can save the textbook language for Twilight."
"Oh stop it." Starlight playfully pushed Trixie away, but failed to suppress a faint giggle. "You haven't even experienced a fraction of Twilight's true vocabulary."
"And Trixie hopes to keep it that way." The light blue unicorn trotted over to the other end of the room where her hat had apparently been blown to and picked it up with her magic. She gave it a few shakes to clear off any dust and plopped it unceremoniously on her head. As she did, however, she noted that the scorch marks lining the walls held an interesting pattern. "Starlight, how did you manage to destroy your walls in the shape of runes?"
Starlight glanced around her room and noted with fascination, and a hint of dismay, that her walls indeed held scorch patterns matching the runes cast in her spell circle.
"I cast those runes so the magic contained in the circle would pool into them and act as the spell's supporting structure." She scanned the room, counting the number of rune patterns burned into her walls, and confirmed there were less of them than the amount she made for the spell. "I think a few of them ruptured, so their collected magic flowed into the other runes, causing them to overload."
She walked over to one of the marks on her walls and tapped a hoof on it. There was still a trace amount of smoke trailing from within. "Once the magic contained in the runes overwhelmed the circle's container, the circle broke and sent all the runes exploding outwards. Normally they would just dissipate into the air if I cast this outside, but since I did this in an enclosed space", Starlight let out a groan of annoyance, "they just ended up burning into my walls. I'll have to clean this mess later..."
Starlight thought back to when she first heard it crack and mentally went over how unstable the spell felt from then on. It must have cracked from the first rune failing. The spell was already done for, I was just overloading the other runes by trying to keep the circle intact. If I had just let the spell go as soon as it cracked, it would have collapsed a lot more peacefully...
"Trixie to Starlight!"
"Wha-?" Starlight shook her head. "Sorry, I was just thinking about something. Did you say something?"
Trixie raised an eyebrow. "Trixie was wondering what you were doing that would need a spell this powerful."
Starlight pondered for a second. "And if I said you don't need to worry about it?"
"Then Trixie will politely ask about it..."
Starlight let out a sigh of relief.
"... the entire day."
Starlight quickly sucked it back in and let it back out as a sigh of exasperation. "Alright, fine. I was trying to help Twilight with a new project she had. She's trying to invent an entirely new base spell which, if she does it successfully, could allow for the creation of thousands of new spells, as well as possibly make some existing ones far easier to cast."
Trixie again cocked her head in confusion. "Trixie has never heard of a base spell before, is that something to do with making new spells?"
"I... think? I've never heard of them either before, might have Twilight to blame for that. But anyways, yes, Twilight's trying to invent a new building block for spell creation, which apparently hasn't been done since before Luna's banishment." Starlight levitated a book from a messy stack sitting at her desk and opened it in front of them.
"It turned out Starswirl the Bearded was the last one to create a base spell after discovering the first version of the teleportation spell worked by creating an exact replica of the target, sending that to the destination, then sending the original to some closed bubble outside our dimension, eventually leading to the original pony's death. That version was much easier to cast and was how most unicorns got around until, somehow, one of Starswirl's students escaped the bubble alongside the copy after their first time casting it. Once Starswirl worked out what was going on, he combined his magic with that of an ancient artifact to erase the memory of how to cast the spell from all other ponies' minds, and all physical traces of the spell's existence was wiped out. Then, with the help of Celestia and Luna's parents, he did something to our world's field of magic to make sure all attempts to cast it would fail. He worked tirelessly for many moons to craft a new base spell, with which he forged a new teleportation spell that folded the fabric of space-time to directly transport matter from one location to another without destroying the original. As it sounds, this version was far more difficult to task and required far more magical energy. In most cases, only a unicorn whose special talent is in magic has the natural magical reserves to cast it. You can still cast it without this affinity, but you'd almost completely exhaust yourself from the effort. Even with a magic cutie mark, the spell can still drain your reserves if not cast absolutely perfectly. That's why you rarely see unicorns casually traveling by teleportation."
After a few seconds of silence, Trixie registered the story was over. "Wait, if he erased all traces of its existence, how do you have... this?"
Starlight closed the book and revealed the cover, eliciting a gasp from Trixie. "After casting the Erasure, Starswirl documented everything that happened in his personal journal. After realizing I can somewhat understand his horn-writing, Twilight asked me to help her translate the rest of Starswirl's journal. After consulting with Princess Celestia and Luna, they all entrusted me with one of the few copies of its translation, since it contains a lot of details left out of our history books."
She floated the book over to her desk and turned back to her friend. "I'm thinking that if I can figure out what calculations Starswirl made during that period, I'd be on the right track to crafting a new base spell. The problem that Twilight, and now I, have ran into is that among these calculations seems to be an unavoidable... division by zero."
Trixie raised an eyebrow. "Trixie may not have Twilight's brain, but isn't that impossible?"
"Mathematically, no actually, there's a concept called limits that lets you theoretically 'guess' a division-by-zero problem by dividing two numbers close to zero, known as an upper and lower limit. You would then divide numbers increasingly closer to zero to see what value this division approaches as the limits approach zero. Unfortunately it's not something I ever studied; I was always just into the spellcasting. Twilight knows more than me about the topic, but even she seems to be stumped."
Starlight's stomach suddenly grumbled, bringing a blush to her face. Trixie noted from the shadow cast by the sun that it was roughly noontime and deadpanned. "Starlight. When did you last eat?"
Starlight's blush deepened and she sheepishly grinned. "Umm... yesterday?" Trixie opened her mouth to speak, but Starlight cut her off. "You know what, I think I do need a break from this anyways. Maybe I'll be able to think about this better after some fresh air and a full stomach. You want some hayburgers? We can talk about this more over lunch." She trotted over to her door and held it open, waiting for Trixie to respond.
Trixie held her deadpan stare for a few more seconds before rolling her eyes and grinning. "Alright fine, Trixie had a light breakfast anyways." As she trotted past Starlight, she fixed her with a cold glare. "But if you spill ketchup on my cloak again, you'll be finding several, and I mean several smoke bombs hidden in your room tonight."
Starlight closed the door behind her as they trotted away from her room, their sounds of conversation becoming more distant and muffled the farther went.
With nopony around to hear it, Starlight's bookshelf finally fell forward with a resounding thud.