Disclaimer, I own neither the Harry Potter series nor any other series mentioned or involved in this. If you believed that I did, you're a few apples short of a reunion.
To whom it may concern,
First, I must congratulate you on somehow getting your letter to such an impossible location and past the containment put in place by my sister.
But my chosen knight and heir needs none of your foalish parlor tricks, as he has studied intensively all the knowledge I have offered him thus far and still learns at an incredible rate. Indeed, he probably has more power in one limb than any of your teachers, and will truly show his worth to the world and those insipid twits who before abused him once I am freed and the lands know their true ruler.
Princess of the Eternal Night,
Year 992, Day 285
There has been an...interesting development this night. I felt the spells that contain me seem to quiver. With a lightning-like crack, I was no longer the only prisoner upon the moon.
It is a strange creature, with forelimbs like the claws of a dragon, only softer, maybe something like a monkey, but more developed. It wears odd and tattered clothes. It also seems bruised and malnourished, limbs seeming thin even for it's diminutive size.
I have no idea what this thing could be, perhaps some new race that has come to Equestria during my imprisonment, but this youngling has...potential. Even in it's weakened state, it was apparently able to teleport through my magical prison, even weakening my containment ever so slightly. Whatever this may be, it bears further study.
Year 992 Day 288
After three days of caring for the unconscious creature, it has finally awoken. It reacted to me with about as much fear as would be expected of a foal facing such supreme power. From questioning and following examination of his dreams and memories (He has confirmed himself to be male), I have learned close to nothing of how the world has changed in my time away. The youngling knows very little, if anything, outside of the house he was raised in. Although he spoke naught of it, I have found him to be both abused and neglected, haunting his dreams are images of what appear to be an especially heavy talking walrus and a creature that seems to be some sort of bipedal donkey who he refers to as Uncle and Aunt respectively. Both appear to have abused him both emotionally as well, to the point where he doesn't know his name, the only constant he is referred to as is Freak.
Examination of the youngling over the past few days has shown he has a strangely strong grip of magic intrinsic to his body.
It worries me that my sister's reign has degraded things to the point where one with such obvious power and potential is allowed to waste away under the unjust heel of obviously lessor beings, one of many things I will apparently have to correct upon my return.
I have decided to try and teach the youngling. It would be a waste not to and could prove to be an asset, as well as a way to fill time, if nothing else.
Year 992 Day 342
The youngling has shown an impressive improvement over the past months. Although he proved difficult at first, given that one of the few things his former caretakers taught him was that magic did not exist. Although a foalish and easily dis-proven idea, they had forced it into his head so much that he had inhibited his own power subconsciously.
After breaking this programming, he has quickly become the prodigy I foresaw. Already, he is able to use his magic to lift things a few times his mass with ease, and has quickly absorbed my teachings, both magical and mundane (It would not do to have an asset without a brain)
Year 994, Day 43
My chosen knight has advanced at an almost frightening rate over the past year, he has taken to his teachings with a fervor and dedication that reminds me much of myself in a younger age.
He has also begun to refer to me as...Mother...
I am unsure how to handle this new situation. Part of me feels righteous indignation, even as my student, for him to presume such closeness to me.
But, I will also admit to a certain...Happiness at this development. This would cement his loyalty and, as loathe as I may be to admit it, perhaps finally having somepony else as company after so long...
Year 994 Day 207
There has been a most surprising development with my student. Where I'd left to slumber my student, I found now a young alicorn colt of dark navy pelt and a mane as black as the darkest night which, along with his still piercing green eyes, was the only thing that remained even close to his original form.
The only explanation he gave was a wish. As he lay down to rest this past night, he wished upon the stars, with all his heart, and the stars answered his wish...
To be my son.
And this wish made him as he is now, the power of the stars above evident in his cutie mark, a shooting star with a lightning shaped tail. He is of elegant stature and gait that any mare with eyes would accept his suit once he has reached the age of courtship.
Now, truly, I must concede, he is an heir of suitable power, and now seemingly of blood, an alicorn.
I have a son, and I shall call him...
Year 995 Day 26
Although he was required to relearn many things in his new form, Star Bolt's already quick absorption of my lessons has accelerated, only slowed by his need to adjust to his now greater power inherent to an alicorn. He has also had learned to fly with incredible ease, seeming natural in fight. In fact, he seems to have become more at home in his new form than his original.
However, he does at times become heavily fatigued and suffer from headaches, I believe he is pushing himself to overexertion. I have decided focus more on theory and mundane teachings to remedy this, for now.
Year 998 Day 260
My gradual wearing away at my sister's spellwork has had another boon. A letter appeared before Star Bolt sent with some odd form of teleportation, powerful enough that, like Star Bolt's arrival, wore down the imprisoning spells.
Assuming this letter truly is meant for Star Bolt, it appears his name was originally Harry Potter, surprising that a foal of such power had such humble beginnings as to be a son of a pottery maker.
I have answered the letter with a refusal, I see no need for my son to attend a school he cannot even reach at this moment to learn this he had probably learned years ago.
Star Bolt's headaches have had a resurgence as of late...
Year 999 Day 230
I have become worried. Star Bolt's headaches have become worse over the past few months, pushing me to the edge of my limited medical knowledge.
He has also begun to suffer night terrors, visions of death, the blood of innocents, his original kind...
I have tried to look into his dreams, but they are so jumbled and turbulent, the only constant I can see is disturbing, something like Star Bolt's original form, but with decidedly serpent like traits, and his eyes...they are the eyes of a madpony, one who kills without remorse or reason.
Year 999, Day 245
I have nearly been locked upon the moon for a thousand years, and now I need to escape more than ever.
I have extensively examined my son in every way I know, and I have found the source of his ailment. A scar upon his brow, something I had long ago dismissed as a mark of his foalish former caretakers. There is something within the scar, something evil that has gripped my son's soul, digging into him like a cancer, and it has been inexplicably been growing stronger in recent months. His magic has grown weaker by the day, as has his body, looking more and more like the sickly creature I found years ago.
I can stall it, contain it, but only temporarily. My power, as it is now, would only feed this darkness and deepen it's roots into my son.
I doubt even my sister could aid my son as he is now, so there is only one hope I can think of, so my hoof is forced. I shall beseech the stars for their aid, as my son did years ago, to break my weakened containment. Celestia will most likely see the signs, but I have no other option. I will not lose my son!
I will have the Elements, even if I must take them from my sister's cooling corpse...
Celestia stepped towards her sister, now purified by the Elements of Harmony, only to be forced back, barely avoiding a strike from the horn of the younger alicorn.
Even in her currently weakened state, Luna, formerly Nightmare Moon, stood with an almost maddened look in her eyes.
"Give...Me...The Elements," Luna panted, her body shaking.
"Sister," Celestia said, hesitantly, "You are not well, your body has been left weakened when the dark forced left you, we should get you to-"
"NO!" Luna barked, her voice shaking the castle, "I need the Elements, Celestia, and I'll take them," She glared at the Element's current holders, "From your dead bodies if I mu-" Lune stopped, her eyes shooting wide as she felt something break, "No," she whispered, tears welling up in her eyes, before she took off in a dash, past the ponies and her sister, "NO!"
Celestia and her subjects followed suit, chasing after Luna through the ancient castle, watching the night princess ascend a tower Celestia recognized as Luna's from long ago.
When the seven mares finally caught up to the night princess, she was in a hastily refurbished room, openly weeping over young, sickly colt laying on a bed.
"Star Bolt! Please, say something," Luna sobbed, "Please..."
The sickly colt could barely open his eyes, their once sharp green cloudy and dull, his breaths shallow, "M-Mother?"
"Yes, my son," Luna answered, nuzzling her colt.
"M-mother," Star whimpered, "It hurts."
"I-it's alright, it will be alright, my son," Luna sobbed, forcing a smile, "My sister has brought help, you will be fine." Walking away from the bed, Luna glared at her sister, and spoke in a low voice, "I do not care what you plan for me, execute me, imprison me again, do what you will, but please," Luna could no longer keep her composure, her head dropping, "Please, save my son, the Elements are the only way to free him from the taint that threatens his very soul, they are his only chance."
Seeing her sister breaking down, Celestia turned and nodded to her student, "Twilight Sparkle, do what you can."
Unsure, Twilight and her friends gathered around the young pony as their necklaces began to glow, an orb of light, every color of the spectrum, enveloping the colt as he began to float.
080-Elsewhere, in another reality-080
Albus Dumbledore steeled himself for the coming battle, knowing it may be his last. Approaching the castle were the forces of darkness, lead by Voldemort, resurrected by the stolen Philosopher's Stone. Staring down his former student, Dumbledore drew his wand.
Luna watched as a dark miasma formed around her son, the Element bearers beginning to strain as it hissed like a snake, coalescing around the young colt.
Seeing the pained expression on her son's face, Luna steeled herself, dredging up what power she had left, she focused it into her horn and charged, ignoring her sister's cries as she leaped into the light, a roaring battle cry echoed as she drove her glowing horn into the shadow.
She didn't care if she died, she would protect her son.
Dumbledore could feel himself tiring as he dueled the monster that was once Tom Riddle. His chances were almost none with Voldemort backed up by the Philosopher's Stone, but he had to try. In the back of his mind, Albus did something he hadn't done since his mother died.
He prayed, he prayed to whatever power was listening for a miracle.
And something answered...
In the middle of the incantation for the Killing Curse, Vodemort dropped to his knees, screaming in such pain that all battle near him stopped. It felt as if something was burning him from the inside, he couldn't muster any sort of thought, let alone cast a spell. Like breaking glass, the dark wizards skin began to crack, light shining through as he tried to fight it off.
He was Lord Voldemort, the greatest wizard to ever live. He was immortal, he would not be defeated.
Voldemort felt a sudden stabbing in his body and something snapped. Every dark deed, every murder, every torture, from the innocents he'd slaughtered to the unicorn's blood he'd sustained himself on, his body and soul burned in the light.
A voice rang out, everywhere and nowhere, loud enough to shatter glass as storm clouds circled above.
"YOU SHALL NOT TAKE MY SON!"
With that, Voldemort erupted in a bright burst of light that cascaded in all directions, sweeping across the battlefield and beyond. Dementors, inferi and Vampires burned away into nothing in an instant, werewolves and death eaters fell to the ground, writhing in pain, unable to withstand the pure power of the light.
For many years after, Wizards the world over would wonder as to what had happened to turn the tide of the battle, the lands, remains and survivors would be analyzed to an insane degree, and they would barely scratch the surface of the light that had literally shattered the darkness. Only Albus Dumbledore had an inkling to the source, the mother whose sacrifice had, again, saved the world.
And even he would be wrong, in a way.
As the light cleared, Luna found herself, no longer in the long abandoned castle, but a beautiful field of flowers of every color and shade, even some she'd never seen on a flower.
The voice startled Luna, who spun around to find her son, sleeping soundly, with his head in the lap of another, one of his original race, a female, she guess, with a long red mane.
"Who are you, and what are you doing with my son?"
The female smiled softly, "Just taking my last opportunity to thank you, your highness, for saving him, and being a mother when I could not."
Luna balked as she was engulfed in a bright light, finding herself back in the ancient castle, standing over the bed as her son's eyes opened.
Luna didn't care what came next, if she was to be a princess or a prisoner, this, by far, was her most important title.