He had been Harry Potter once, a very long time ago. A time when he had friends and loved ones. A time when magic and wonders were an everyday occurrence for him. But that time had since passed and it had been a few centuries now since he was the only one left, the only magical being in the world. Immutable. Unchangeable. Eternal.
And yet, for all his powers, he had been unable to stop it. The extinction of magic. Not in his world, at least.
But he had strived to stop it, in every other world similar and yet somewhat different from his own. Little differences sometimes, based on the choices some key people had made, and sometimes very big ones. He had succeeded sometimes, and sometimes he had failed. Changing things here and there, manipulating the events to influence the outcome.
He had seen worlds where Ariana Dumbledore had never died, where Dumbledore and Grindelwald had stayed united and went about to rule the wizarding world together, until Tom Riddle had risen to power. A clash of titans, with the dark side divided and the light side somewhat coming out stronger than ever and the muggleborns had multiplied, with more and more muggles finding out about the existence of the wizarding world and then, of course, they had been discovered.
He had seen worlds where Tom Riddle had been raised by his mother Merope, had grown up to become Minister of Magic but, as great of a leader as he had been, he had underestimated the danger the muggles represented and, once again, they had been discovered.
He had seen worlds where Harry – or another version of him, at least – had risen to become a Dark Lord, or Lady, ruled the wizarding world but even then, the muggleborns had been too many, and with too many muggles in the known to do anything about it in time.
The best outcomes had happened when Tom and Harry had joined sides, but even then, in the 1990's, it had been already too late. Even with the muggles not finding out about them, the new generations of wizards and witches were being born with weaker and weaker magic every year. Too much inbreeding, but also too many muggleborns marrying with half-bloods or other muggleborns. Too many ancient bloodlines losing their Dark or Light magic and instead acquiring a weaker, neutral magic, neither light or dark.
Harry had in fact observed and then studied at length the difference in magical blood, from muggleborns, half-bloods and purebloods, and then studied the muggle blood as well. He had found out, much to his dismay (that was many centuries ago, when the problem of the weakening of the magic had first presented itself) that the dark pureblood lines did have a point in discriminating against muggleborns after all.
The offspring of a several generations pureblood and a half-blood, muggle, or muggleborn would produce more times than not an above average magical being, who acquired the magical affinity of the pureblood line, light or dark. That was because, when the pureblood lines became too inbred, their magical offspring – while still maintaining the magical affinity intact – would begin to be born with a below average magical power. In that case, an influx of new blood, whether from muggles, half-bloods or muggleborns, would help to renew the line and the offspring born from such a union would be much stronger than would be normally possible (Harry, Voldemort and Snape were very good examples of such a thing). The problem was born, though, when the offspring of a pureblood and a half-blood, muggleborn or muggle would produce a child with another half-blood, muggle or muggleborn. The child from that union would lose the magical affinity and their magic would be weaker than both their parents and neutral.
Fortunately, Harry had found a solution for all of that. He had invented spells for it. To purify the magical blood from the harming elements that caused weaker magic. But by that time, he had been too late to do anything about his own world.
In the other worlds, he had interfered only in small ways. Sometimes he had made things better, sometimes even worse.
This time, he wanted to interfere in the biggest way he could think of.
Harry could only jump in specific moments in time and in different dimensions but he couldn't stay there long, a few days at the most. But a few days was all he needed. Luckily, he could also bring objects and even beings – animals, people – from one time or dimension to another.
He knew that what he was about to do could perhaps have unforeseen, maybe even devastating, consequences and yet, he needed to know. He needed to try and see, if, in at least, one world, the extinction of their race could be avoided.
He apparated in front of number four Privet Drive, the night of the 31st of October 1981, in a world where there was no boy-who-lived but there was a girl-who-lived instead. Everything else was the same. Voldemort had still momentarily fallen but had still been alive because of his horcruxes, Pettigrew had still framed Sirius and the Potters had been killed. And now Hagrid was about to bring little Anna Potter to the Dursleys house, and waiting for her were Dumbledore and McGonagall.
Harry waited, patiently, underneath the Cloak of Invisibility, one of the Deathly Hallows, that was still perfectly untouched, even after thousands of years.
He tuned out the conversation that, at that point, he had heard hundred of times. Finally, Hagrid left first, then McGonagall and, finally, Dumbledore as well.
Harry picked the bundle up from the front step of the replica of the house he had spent his childhood in, his personal prison, and looked at the baby wrapped in blankets. She was beautiful, even at just one year old, with a tuft of black hair on her head, and soft-looking, milky skin. And when she opened her eyes, Harry wasn't surprised to see emerald green eyes looking back at him. The only thing marring that perfect face, was a scar in the shape of a lighting bolt. But no matter, he would take care of that soon.
Harry smiled at the child in his arms and picked the letter Dumbledore had left from between the folds of the blankets. He barely needed to think about it before the paper turned to ashes in his palm.
Not wanting to linger too long in Privet Drive, he disappeared, with the child still in his arms, and he reappeared in muggle London, in front of a derelict building. It was the 31st of March 1928, exactly one year and three months after Tom Riddle was born. In this particular reality – different from the one he had just left behind –, Merope hadn't died in childbirth, and Tom had known the warmth and love of a mother, brief though it was, thing that Harry knew would be enough for Tom to grow up capable of love, though it wasn't an emotion that would ever come easily for him, being born because of a love potion and all.
Merope would die soon, Harry knew. A few more months left. He also knew that she would find herself in front of Wool's Orphanage exactly the 13th of May and that, after leaving the child to the matron, Mrs Cole, and after using the last strength she had left to tell her Tom's full name, she would die there.
This particular reality didn't have a Harry Potter, or any version of him. The child of the prophecy would grow up to be Neville Longbottom, while Lily and James will never marry in this reality. Having a version of Harry Potter here would not cause any kind of time paradox.
Harry entered the house, both him and the child covered by the invisibility cloak, and observed the two people sleeping inside. Harry, to make sure they wouldn't wake at an inopportune moment, put them under a sleeping spell.
Then he put Anna in the same crib Tom was sleeping in and put her under a sleeping spell as well. He didn't want her to wake either since what he was about to do could be a little painful for her.
He had invented numerous spells during his incredibly long life. One of those spells was what he had named the 'blood adoption' ritual. He had invented this spell to solve the problem of half-bloods and muggleborns turning light and dark magic into weaker, neutral magic. It was a spell that would allow pureblood lines to adopt muggleborn and half-blood children without running the risk of losing their particular brand of magic over time and the specific characteristics of every bloodline (like the Blacks having metamorphmagus abilities or the parseltongue for the Slytherin line) while still maintaining powerful magic. This spell allowed the person whose blood adoption was casted on, to acquire the blood – and therefore the magical characteristics particular for every magical bloodline – of the family they were going to become a part of.
With such a spell muggleborns and half-bloods would be turned into first generation purebloods, erasing completely the muggle blood but still bringing 'new' blood at the same time – therefore solving the problem of inbreeding. By erasing the 'muggle component' of the blood, in fact, it neutralized as well, that particular element – a variation of the one present in muggles that was the cause of them not having magic – that would turn light and dark magic into weaker, neutral magic, after several generations of half-bloods, muggleborns and muggles breeding among themselves and with the old pureblood lines. This way, both light and dark magic present in the different bloodlines was preserved.
Such a spell would also solve the problem of squibs. There would be no more squibs, because such a spell eliminated the element present in the blood – similar and yet opposite from the one present in the muggles – that blocked squibs from performing magic. That would also stop the pureblood lines from abandoning squibs in the muggle world, as it often happened.
Harry had, moreover, found out, after numerous researches, that someone who descended from a squib, usually two or three generations back, would be born with magic. Such magic would carry the same characteristics as the one from the family of the squibs – therefore light magic or dark magic depending if the family was dark or light. Those particular individuals were believed to be muggleborns but they weren't. They were, as well, first generation purebloods and therefore able to safely mix with pureblood lines.
Harry shook his head to dispel the technicalities of magical and muggle blood and turned to the problem at hand. The spell he was about to execute was similar to the 'blood adoption' spell but different. With this spell, in fact, Anna would 'adopt' the Gaunt – and therefore Slytherin – blood while still maintaining the muggle blood that came from Lily Evans. Such a thing was necessary because Harry planned on turning Anna into Tom Riddle's sister, twin to be precise.
They wouldn't really be twins, or siblings for that matter, not genetically, at least. But magically, they would become brother and sister. Their magic would be a perfect match of each other, even more than it was normally between Voldemort and the Potter child, because of the Potter child being a Horcrux.
With such a spell, even the goblins at Gringotts would be fooled into believing that Anna and Tom were siblings. After all, in the blood test they did at Gringotts, only the magical bloodlines would appear. For both children, the bloodlines of Gaunt, Slytherin and Peverell would appear and that was all that mattered.
Merope had already performed the simple naming ceremony for Tom. So, Harry needed to do the same for Anna. Her name was Anna Potter for the moment but he would do a spell to overwrite it, so to say.
Harry worked for hours – the spell was very complex and long. He had brought five phials of blood taken from Morfin Gaunt who was in Azkaban at the moment but not for long.
Before he could safely use it, though, Harry needed to 'purify' it from the harming elements present in it, caused by the inbreeding and the extremely low magical component. Once done with it, this blood would be as close to the actual blood of Salazar Slytherin as it could get.
With a few murmured words the blood was absorbed inside Anna's body. The child glowed gold for a few, long seconds and then the light disappeared.
Now that part was done, Harry started to work on the second part of his plan, with another spell of his own invention.
When he was done, a light once again enveloped the child, this time of a dark red colour and the scar on her forehead disappeared, and with that, the horcrux inside her. The piece of soul belonging to Voldemort and Anna's own soul had been fused together, forming another, different soul in some way. No more a horcrux, not part of Voldemort anymore, but not completely Anna Potter either. Someone new, someone different from the child Harry had been. But still someone deeply connected with Tom Riddle nonetheless. Kindred souls now, their affinity would resound deep within themselves, for both Tom and Anna.
And now for the last part. The naming ceremony. But for that, he needed Merope. She was the only one who could name Anna, so that, even with the surname Riddle, Anna, like Tom, would be recognized as part of the Gaunt bloodline and therefore as a descendant of Salazar Slytherin.
But to do that, he needed to modify Merope's memories, to make her believe that Anna was really her child. It was cruel maybe, but necessary. And Merope would have another child to love, with the little time she still had left; there were worst things in the world.
Hours later, when the sun was just starting to rise above the horizon, Harry was done.
He left the house with a smile on his face, leaving behind Merope, her child Tom and Tom's new sister Anna Morven Riddle, and disapparated thousands of miles away, to reappear on Samson, the largest uninhabited island of the Isles of Scilly, an archipelago off the southwestern tip of Cornwall. There, choosing a place that looked out over the sea and the white sand below, he searched in his pockets for the perfect shrunken replica of the Manor House that had belonged to House Slytherin and then House Gaunt till the 1100's, when they had started to lose their fortune. He put it on the ground and then reverted the spell, returning it to its actual size. Then he spent hours working on the wards, both for the manor and the entire island, making them even more unplottable and impenetrable than Grimmauld Place under the Fidelius Charm. He made the island impossible to reach by sea, invisible to muggles, and impossible to find to everyone who didn't already know where it was. The only way to reach the manor and the island was through portkeys, which he created for both Anna and Tom. He also connected the manor to the floo network, but only one way, from the manor to the outside world but not the opposite, so the manor couldn't be reached through the floo.
The manor came with a Quidditch pitch, stables (empty at the moment but he planned on bringing different species of winged horses - abraxans, aethonans, granians and thestrals - to fill them up from various other dimensions) and and an enormous magical garden park with a maze. He also needed to bring house-elves to tend to the house and the lands of the island that surrounded it. Once inside the manor, he filled the empty shelves of the library with copies of all the books he had spent centuries accumulating, and copies of the books and journals he himself had written as well (those were all in Parseltongue) – he signed the copies with a made-up name, Malek Gaunt and made them look centuries old. When he was done, the library inside the manor was even more extensive than the Hogwarts library and the one in Grimmauld Place put together.
Then he disapparated from there to appear in front of Gringotts bank, in Diagon Alley. In Gringotts, looking like an extremely old man, he introduced himself to the goblins as Malek Gaunt, saying that he wanted to open a vault in the lowest level of the bank, and therefore the one with the most protections. The goblins, at first, didn't want to comply with his request, but once he showed them all the treasures he had with him, they immediately changed their tunes.
He was assigned vault 17, and inside he put the gold he had accumulated during the millennia he had lived that didn't come from the vaults he had inherited from his parents and Sirius, which was more gold than could be spent in one hundred lifetimes.
Beside the gold, he also left inside some particular artefacts: the Cloak of Invisibility – not his original one, but one that came from this same reality (he had stolen it from the Potter family of that time and left another Cloak of Invisibility from another reality in its place – there were technically two Cloaks of Invisibility in the same reality now, but only one could be used together with the other two Deathly Hallows of that reality to become the Master of Death), the Gaunt ring with the Resurrection Stone – that one he had taken from Morfin Gaunt –, the Slytherin Locket he had 'retrieved' (meaning, stole) from Borgin and Burkes before modifying the shop owners' memories, two mirrors charmed to work like the two-way mirrors Sirius had given him so long ago and that he still regretted not using when he should have, and a map of Hogwarts with the same spells of the Marauders' Map but with much more secret places and passages than the ones in the map his father, Sirius and Remus had made (included the Room of Requirements but not the Chamber of Secrets which was, technically, not in Hogwarts but underneath it). Beside that, he also left many other Dark Arts books (included some Necromancers' grimoires), very old texts which were basically impossible to find anywhere else, most of them written in Parseltongue.
Once that was done, he left specific instructions to the goblins that no one could know this vault had been opened only today or who had opened it. He made sure to tell them that he had opened the vault for Tom and Anna Riddle and only these two people could have access to it, and eventually their children and grandchildren, but no one else in the Slytherin, Gaunt or even Peverell line. The vault would be, in fact, spelled to open only for those 'worthy' of it – with enough magical power to be considered real descendants of Slytherin. The inheritance for the two children would also include the Manor in Cornwall that he had dubbed Slytherin Manor. The children could inherit at 11 years old, instead of the usual 17 – the age of majority in the Wizarding World. This way they would have a place to return to each summer after every year at Hogwarts, instead of being forced to stay at the orphanage and they would have as much gold as every other pureblood child from the old lines, more even.
He wished they didn't have to live so long in the muggle world, especially in an orphanage, but it was necessary. They needed to know the enemy, who they were dealing with really, so that they wouldn't be as ignorant as the other purebloods and they would be able to choose the best way to act against them when the time would come.
Once the business at Gringotts was taken care of, he spent the next day going back and forth between other realities and this one, to procure the winged horses and the house-elves (which were now sworn to House Gaunt and answered only to them) for the manor. The third day he spent building things on the island that could make it more habitable, or fixing up what was already there. When he was done, the island, which was already beautiful on its own, looked like a magical paradise directly out a fairytale book.
Harry nodded in satisfaction. Everything was ready. He did all he could. Now, the rest was up to them. He hoped this time he had made the right choice.
"Good luck, Tom and Anna Riddle. You're my only hope." Harry whispered to himself before disappearing. He would be able to return only decades later and only then would he know the consequences of his interference. For now, all he could do was wait.