Before you even open your eyes, you feel... different. It's as though a heat is coursing through you, and a pressure is weighing down on you. You feel, well, powerful, you suppose. With a deep inhale you open your eyes and assess the situation around you.
You don't remember standing up, but you are definitely back on your feet. Your horn and wings are still visible, but you've never seen them glow this bright. To your left and right, the four alicorns are struggling to get back on their hooves, but their attention is turned squarely on you. They all share the same shocked expression. Beneath you, Celestia still lies prone on the floor, though she still seems conscious. Her cheeks are stained with dry tears, but it's hard to read exactly what she's feeling based on her face. Her eyes are practically glazed over, as though she has just come to a realization. Most importantly, however, is what is right in front of you. The source of the pressure is clear, as the colossal form of the First is currently bearing down on you. And yet, you are perfectly fine.
For the first time, you can clearly see an emotion on the First's face: fear. Her massive front legs, which she had used to stomp down onto Celestia and yourself, are currently above you. It seems that, somehow, you caught them, one leg in each hand. Your outstretched arms are holding her at bay, but surely you aren't strong enough to hold her back, right? And yet, there you are. You don't really understand where this power is coming from, but right now, you don't really care either. With a cocky smirk, you let out a single confident chuckle. Let's see just how far you've come.
Not letting go of the First, you concentrate on a familiar spell and watch as about a half-dozen grape-covered vines sprout from the ground on either side of the First and promptly shoot towards her hind legs and torso, wrapping around her and squeezing tightly. You hear her let out a quick grunt before you tighten your grip on her hooves and attempt another spell you haven't used in a while. Beneath the glowing white of the First's hooves, your hands begin to turn a bright orange before flames burst out of them, shooting upwards around your foe's front legs and reaching up to the base of her neck high above you. She wails as you watch her finally recoil, and you let go of her hooves. She stumbles backwards just a bit, not having much freedom of movement thanks to your vines, but you aren't planning on giving her any respite. With a quick flash you shoot another magical beam from your hands, this time appearing much bigger and brighter than earlier. It impacts right at the center of the First's chest, and it seems that your attacks are finally starting to hurt her. Her commanding voice rings out throughout the chamber once more.
"How? What sort of magic is this? I am the First! Only the First is eternally the First!"
Her horn glows bright once more as she lets out another attack at you in desperation. You aren't quite sure where your sudden burst of confidence is coming from, but you don't even bother to create a shield to protect the mare below you. Instead, you simply smile and watch as the beam nearly hits you, predicting when exactly it will hit. In one fluid motion, you channel magic into your forearm and with a simple waving motion, you successfully redirect the attack to impact the floor behind you instead.
"W-what?!"
Not wanting to lose the momentum you have going here, you turn to look at Twilight, Cadance, Luna, and Sunny, who have now all regained their footing and are looking at you expectantly.
"Altogether, one last time?"
They all give you a nervous smile and nod, grouping up at your sides once more. For a few moments there is silence as the five of you gather magic in preparation for one final, combined attack.
This is it. It's all or nothing.
"No! I will not allow this!"
Now visibly distressed, the First mirrors your actions, channeling as much magic as she can into her horn. For your part, you prepare your arms for the spell to come. With your feet planted and your teeth grit, you take a deep breath using the special breathing technique that Twilight taught you when you first came to Equestria.
All at once the chamber is filled with light as six creatures release their most powerful spells at the same time. The First's blindingly bright white magic impacts the much more colorful combined magic of you and your alicorn comrades. The pressure is intense, and it takes all of your focus to not only keep the spell going, but to do it in such a way that it properly aligns with those of your allies. The clashing spells seem to be an even match, with the magic meeting at some point in the middle. There you struggle for what feels like hours (but is almost certainly minutes at the most). Eventually, though, fatigue begins to set in. As the First's magic slowly begins to overtake your own, you take a quick glance below you. Celestia is still sprawled out on the floor beneath you, carefully watching the fight unfold. She seems to be in shock. You don't blame her. She has had... a lot to process in the span of a day. Looking at her thin figure, you make sure to commit her pained expression to memory. She doesn't deserve this. That's why you're here, after all. You aren't going to let anything happen to her.
Emboldened by these thoughts, you double down on your magic with might you didn't believe possible. In an instant, the tides turn in your favor. In fact, it seems that there is little contest. All at once you watch as the colorful combined magic of yourself and the other alicorns obliterates that of the First, slamming against her with enough force to send her massive form flying backwards. The sounds of shattering glass and crumbling marble fills the chamber as the First is thrown through the stained glass window on the back wall, your magic seemingly doing great harm to her while also pushing her back. Still, with a being as powerful as her, you know you can't stop, and you try to focus on keeping up the attack for as long as possible. As the First flies backwards into the sky, you hear Luna begin to speak as best she can through gritted teeth.
"This... won't be enough! She's pure magic! No matter how long we keep this up, she'll survive! There's nothing in Equestria that can finish her off!"
While Luna's words are not lost on you, there is little that the five of you can do but continue your assault. By now she has to have been flung far into the orange, sunset sky. Your arms are in agony now, and it is taking everything you can to keep up the attack while you try to process everything that's going on. There's nothing in Equestria that can finish her off? That's probably true, and also probably why she is so adverse to your presence seeing as you aren't from Equestria. But what else can you do?
As you look past the newly formed hole in the wall (or, at least, what little you can see that isn't obscured by your magic), your eyes settle on the sun, which Twilight had apparently left half-set before coming to your aid. An idea begins to form in your head, but you're going to be making a gamble. Still... you trust that she'll be able to pull through.
"Tia!"
"H-huh?"
Still on the floor, Celestia looks up at you with shock and confusion.
"Please, we need your help!"
"I-I'm sorry! She already drained most of my alicorn magic! I... I am weak! There's nothing I can do!"
"That's not true! You said it yourself, even before you were an alicorn, you got that cutie mark all on your own! You're so much more than what the First has given you! You always have been! Please, we need you!"
She does not respond. Instead, she holds her mouth agape in shock for just a moment before she closes both it and her eyes. Then, through great pain, struggles to stand. She stumbles more than once on her way up, but with one final grunt, she's finally back on her hooves. Leaning on you for support. You watch her horn slowly begin to glow. The glow is faint, but there nonetheless.
"That was you in my dream all those years ago, wasn't it?" Although gradual at first, everycreature in Equestria watches in awe as the sun, already halfway below the horizon, slowly begins to rise back up into the sky. Tia holds her eyes shut tight, obviously in great pain as she casts the spell that she is most known for. The very spell that got the First's attention to begin with. "...Thank you, my sunshine. You've done more for me than you will ever know."
Far, far in the distance, you can see the outline of the edge of your attack, now carrying the First beyond the stratosphere. As if on cue, your vision is filled with sunlight as Celestia finally finishes moving the sun, which now rests directly in the First's path. All of you begin to yell as you use the last of whatever strength you still had in one final push.
In that moment, the sound of a distant yet unimaginably huge explosion rings out across the planet. The sky is filled with thousands upon thousands of colors as pure magic explodes out of the sun and across Equestria, covering the land in a beautiful, picturesque harmony of color. The five of you finally drop your spells. Your arms fall limply at your sides as you all try desperately to catch your breath. Sunny and Cadance are forced to sit down, while you turn your attention towards Celestia, still leaning against you.
Celestia, the love of your life, looks back at you. Her magenta eyes meet your own, a mixture of anxiety and relief and sadness and joy all visible in her expression. Through your strained breath, you give her a smile, which she happily returns. Your smile isn't meant to mean anything. You aren't trying to comfort her, or add some much-needed tension relief or anything like that. No, your smile is the smile of someone who just did the impossible. Against all odds, you faced off against a goddess and saved your wife-to-be from certain death. You've finally fulfilled your promise to protect her, and it seems that in her own way, she did the same for you. There is nothing left to stop you from chasing the future that you've always wanted. With that thought, that wonderful thought, you feel your consciousness begin to fade once more. You embrace Celestia in the tightest hug you can muster, which she wordlessly returns as you both fall to the floor.
You've done it.
You've won.