This is a "Six Years Later" epilogue to Harry Potter and the Methods of Rationality by Eliezer Yudkowsky that I wrote a while and back and am just now getting around to posting here (it was previously posted on /r/hpmor). It contains ending spoilers for that story, and for six other books that have not been (and will not be) written. As should be clear from the title, it is not meant to be taken entirely seriously.

"And I'm betrothed to Hermione Granger, and Bellatrix Black, and Luna Lovegood, and oh yes, Draco Malfoy too..."

Harry stood in front of a large whiteboard, thinking at it as hard as he could. There had been a time, years earlier, when he'd used paper and pencil to work through a hard problem. Later, it had been a magically enchanted quill scribbling across parchment as quickly as he could speak. Now it was the whiteboard, which displayed his very thoughts, putting up the concepts as they came to his mind, pulling needed information from the library, and quickly doing any of the more difficult maths. Harry had tried using a computer - it was hard not to think of them as muggle computers - but it would be a decade at the least before they could exceed what Harry had here. The whiteboard was an extension of his thoughts, a way of adding onto his cognitive power. What he'd really wanted was something that could make him smarter, but they hadn't found anything like that yet. They did have a diadem that augmented thought processes, but Hermione had told him that he wasn't allowed to use it until it had been thoroughly tested, so that had been that.

One small corner of the whiteboard had a blinking red light, which he put up when he needed to be firmly and viscerally reminded of the importance of his work. There was a device in the Headmistress's office that counted the number of "let's call them sneezes" (it had taken Harry longer than he'd have liked to admit to catch the meaning) of all of the left-handed witches in France. The blinker worked on a similar principle, but instead of tracking left-handed witches it tracked every sentient creature on and off the planet, and instead of "sneezes" it tracked deaths. In the four years since he'd put that bit of astonishingly simple magic together, he'd noticed it slowing down. The raw numbers showed that they were preventing one in every ten deaths (with another one in three becoming "reversible" deaths for when the state of the art had advanced beyond where it was now). It still felt like a drop in the bucket.

A small chime sounded, and the whiteboard folded itself away. Work time was over, and Harry sighed with mingled relief and frustration. Every day was a thirty hour day for Harry - six objective years ended up being seven and a half subjective ones. It had been difficult, in the beginning, to feel like he could spare time for leisure. His solution had been to give fun and work different time slots, so that when the chime sounded he could fold up what he was doing and not just go looking for the next problem that needed his attention. He shifted his mind away from the work with only a twinge of latent guilt.

He stood up and stretched out, then began his customary tour of his domain.

Six years had changed Hogwarts, though less than might have been expected. It was still soaked in magics that were covered by the Interdict, and the Interdict had proven stubbornly resistant to the combined intellect of the Bayesian Cabal. The quidditch pitch now doubled as the interplanetary launching platform, and through the unusual but now well-understood geometries of Hogwarts, it was sometimes possible for it to be one or the other depending on which way you entered from. A new turret had been raised from the depths of the Slytherin dungeons, made of a modified tree which Neville Longbottom had bred for the purposes of terraforming Mars. The Headmistress had a row with him and the well-intentioned students who didn't think that Slytherin should be confined to a literal dungeon, and eventually the tree had gone from being a temporary crisis to a permanent living space. There were third-years now who just thought that the Slytherin Lignum Tower was simply The Way Hogwarts Was. And there were quite a few more students in Hogwarts these days, since it had become the single most prestigious place for a wizard or witch to learn their craft, not to mention that Hogwarts now offered extremely generous scholarships to anyone with the slightest interest in attending. The hallways were filled with a confusion of languages, which was redoubled by the small homunculi that perched on students' shoulders and translated whatever was being said. Harry made a mental note to talk to the Weasley twins about their creations, and hopefully find a way to simply have the creatures speak into their owners minds instead. He halfway imagined that they could have done so all along - they had been the campaigners behind "Keep Hogwarts Weird" for their entire seventh year. Harry attributed the current personal fashions to the enduring legacy of their time at Hogwarts.

He found Luna standing on one of the fifth floor balconies. She was a monkey with small wings and the head of a crow, which was one of her less whimsical forms. She wore her customary pouch which was slung across one shoulder (which she referred to as a "Pouc" for reasons known only to her) and had on something resembling a robe (since the Headmistress had often remarked that being an otherkin didn't absolve a person of the need for wearing pants in polite society). She'd kept her hair a silvery white, and smiled at him in a slightly unfocused way that he was fairly certain wasn't accurate to a crow's anatomy. Duplicating the Philosopher's Stone had so far proven impossible, but a variant based on the underlying principles had been developed which allowed for safe human transfiguration of a single bonded subject. It had been four years since those had gone into general circulation, and now, at least at Hogwarts, a substantial fraction of the population switched around what they looked like whenever a random whim struck them. The Headmistress was displeased by this development, but had put yet to put any serious restrictions in place save for the rule against impersonation (and of course, the rule about wearing pants).

"Hello Luna," said Harry.

"Oh, Harry," said Luna. Her voice was light and airy, and very uncrowlike. "Did you know that the gilded Snauffle-Quatchers hatch today?"

"No," said Harry. "I had no idea." Half of what Luna said was nonsense, but she was friendly and kind, and Harry had grown to enjoy her company a great deal. "Did you know that today would be my graduation day, if we still had those?"

"Of course," said Luna. "I'm a ravenclaw, just for the occasion." Harry realized that her head was meant to be a raven's, not a crows. He saw enough of these fanciful forms that he didn't look too hard at them.

"Any new prophecies for the end of the year?" asked Harry.

"None I can tell you," said Luna with a sigh.

Luna Lovegood had come to his attention in his second year at Hogwarts, after he'd made the connection between things written in the Quibbler and the events of his first year. Dumbledore had sealed the Hall of Prophecy to him, and while Harry could understand what Dumbledore had been thinking, it was difficult to find a way around fate without knowing where fate was standing. He had ignored the Quibbler for a long time, thinking that it was simply tabloid nonsense, but the coincidences had stacked up too nicely. Once Luna had started writing a serialized novel published weekly in the Quibbler titled Harry Potter and the Wayward Scion, he had brought her into the Bayesian Cabal, more out of necessity than any real belief that he could teach her rationality. Her novelization of the events of his first year had included details that she shouldn't have had access to. Harry had wanted to prevent the final chapter from being published, but Hermione had argued with him about the importance of a free press, and eventually he'd had to agree. It was a full and accurate accounting of what had happened in the graveyard, and no one had paid it much attention save to say that it was in poor taste and not as good as the rest of the book.

"Well," said Harry. "If there's anything that comes to mind which you think won't cause some undue effects somewhere down the line, let me know."

Luna moved forward and slipped her monkey paw into his hand. "Today is an important day, Harry. Not for the world, but for you."

"Er, because it would have been graduation? Or some prophecy that you can't tell me?"

Luna shrugged, and to the extent that a crow could smile, she did. "It's the capstone of my latest book."

Harry leaned forward and kissed her on the beak. "If you're feeling more human later, I'd like to have some company tonight. We can pretend that it was a proper graduation and throw a celebration."

Luna's crow head bobbed up and down, and she leaned up to give him a quite literal peck on the cheek. "I shall be there with bells on."

Harry took one last look out the balcony to where a group of students were having debate in one of the courtyard, then left Luna behind and continued his tour. Things had turned romantic with them only recently, and he'd found that it had added a dimension to their friendship that was sorely needed. He wasn't sure that he really understood Luna, or the process by which she got her prophecies, even after reading her novelization of Harry's second year where she played a starring role (Harry Potter and the Prophecy Engine). He only knew that it was nothing like Trelawney's deeply intoned and cryptic messages, and that it was accompanied by a great deal of completely useless and incorrect information, which largely informed who she was as a person. He'd grown to like her a great deal more once he'd realized that it wasn't just pointless woo-woo like his mother used to follow.

His next stop was to see Hermione, who was working in labs that were connected to Hogwarts through a small strip of subspace that looked just like an ordinary corridor. He found her at her workbench, floating just above the floor. As soon as she'd known it was a possibility, she had gotten the same incantation on her bones that Tom Riddle had, and she could often be seen flying around Hogwarts with her innocence aura trailing behind her. Her auburn hair had straightened as they'd grown up, and her front teeth weren't so comically large anymore. She was radiantly beautiful. The unicorn aura and strength of a hundred men only added to that. A small black cat with a metal forelimb sat patiently on the floor next to her.

"Work hours are over," said Harry. "Did you miss the chime?"

"I must have," said Hermione with a frown. She set down her tools and stepped away from the workbench. "I'm trying to solve the Obliviation Problem."

The small black cat by her feet exploded in fur and fabric, and shortly thereafter Bellatrix Black was standing where the cat had been. The woman that Harry had pulled from Azkaban six years ago had been deathly pale and so skinny she looked like she was about to snap. Now she wore the body of her seventeen year old self, and the damage that had been done to her was almost entirely reversed. The Wizengamot had called Bellatrix Black unredeemable, but Harry had brought her into his Cabal anyhow, and proved them wrong. In retrospect, he hadn't been quite prepared to undertake her rehabilitation in his third year (Harry Potter and the Faithful Servant) but he had learned a lot about himself in the process, and despite the bumps in the road, Bellatrix had been drained of the darkness that suffused her. The last remaining piece that tied her to her old life was the metal arm, a final gift that Voldemort had given her when he'd taken her old one from its socket, but it would have been dangerous to remove, and besides that it had a number of definite advantages over an arm of flesh and blood. She had also been a beneficiary of the experimental metamorphmagus v2.0 program, having lost her old Animagus form in Azkaban, and often took the shape of a black animal with a metal arm.

Hermione Granger could bend steel with her bare hands, clipped her nails with the Sword of Gryffindor, travelled the solar system via Phoenix, and was unkillable by anything short of Avada Kedavra, and not even that if she had even the slightest preparation. Bellatrix Black had an arm made of starmetal that could block Fiendfyre, could take the form of any creature known to her in the blink of an eye, practiced Legilimency with her eyes closed, and for reasons that were still not clear, got eight hours to the Time-Turner instead of the usual six.

Together they fought crime.

The Obliviation Problem had been troubling Hermione for a long time. In short, it was possible for a wizard to do whatever they liked to a muggle without regard for things like consent or ethics, and then erase all their memories of it after the fact. This made it nearly impossible to realize there had been a crime at all. Under the old regime, the response had simply been to shrug and say that these things happened, with the unspoken agreement being that it was practically a victimless crime. Hermione had reformed the Department of Memory Modification over the course of three months (Hermione Granger and the Amnesia Codex), but that left every other wizard on the planet to deal with, and the only real stride that had been made towards stopping the problem had been letting everyone know that Hermione Granger took that kind of thing seriously. Eradication of anti-muggle crime seemed impossible short of panopticon surveillance or making every wizard take an Unbreakable Vow, neither of which were currently practical.

"I'm sure you'll figure something out," said Harry. "You always do. How are the muggles?"

Hermione shrugged. "I think they're finally coming to accept that they're not going to figure out the healing. They're calling it 'Sudden Recovery Syndrome' now, and for all that it baffles them, no one is close to finding out the truth. Even if they did, we have buy-in from the major muggle powers. Oh, there was an earthquake near Delhi, but the house elves handled it." She hesitated. "Bella and I stopped a sex trafficking ring in northern Europe this morning, but I sealed most of those memories away. I think it was fairly bad, as those things go. A forest fire in California, a flood in Paraguay, an attempted bombing in Russia that we stopped with Time-Turner. But no wars, no large-scale conflicts, and I'm fairly certain that all the muggle leaders are finally taking us seriously." She bit her lip. "We're going to have to break secrecy one of these days."

"One day," agreed Harry. "Once we know that we can do it safely."

"Alright," said Hermione. "It's just that the casual obliviation of muggles who have seen too much is making the Obliviation Problem harder, and that manpower could be put towards other things, and -"

"I know," Harry said gently. "But that's a work discussion, and it's not work time right now. Agreed?"

"Agreed," sighed Hermione.

The Statute of Secrecy had been a point of contention between them for a long time. Hermione understood his reasons for wanting it in place, and even agreed with them, but she was considerably less happy about the deceptions that it required. The Obliviators now sealed the memories away instead of wiping them entirely, but Hermione was sceptical that those memories would ever be restored.

They had fallen in love faster than either of them had expected. They had known that they loved each other, but actually being in love was an entirely different thing. They'd gone about it in a haphazard way, and the right methods of negotiating those feelings were only obvious in retrospect. If his experiences with Quirrell had taught him that INT was nothing without WIS, being in love with Hermione had taught him that CHA wasn't as much of a dump stat as he'd thought it was. Even after they had been in love for a while, after it wasn't such a surge of emotion to see each other, and when everyone knew that they were a couple (with all the media attention that had gotten them), there were still more things to negotiate. That they had finally gotten to a place where they could have serious, legitimate arguments with each other and not have it feel like the End of Everything was the biggest sign that they had really and truly navigated those minefields.

And it was because of those experiences that he had been able to negotiate his complicated feelings towards Bellatrix. Her story had been heartbreaking, and he'd only want to help her become the person she had been meant to be all along. He wanted her rehabilitated instead of stuck in the prison they'd built to replace Azkaban. She, on the other hand, recognized him as the lord and master she'd dedicated her life to. He'd been fourteen years old, and barely mature enough to deal with it all, but he knew that he had to help her, and that he was the only one that could do it. It had taken three years to untangle the improper bonds that she imagined having with him, but after that was over, she fell in love with him anyway. She loved him for being the sort of person who would show such patience and kindness when there was no clear benefit for him, for coming into her bedroom and sitting with her when she had night terrors, and for standing up for her in front of the Wizengamot. It had taken a long time for them to be able to treat each other as equals, but it had, eventually, happened. And they too had fallen in love, though it was a love of a different flavor.

"Draco has been acting oddly these days past," said Bellatrix. She had a high, sing-song voice which the years had stripped of its cruelty. She and Luna had gotten along fabulously, and could often be found together.

"Oddly how?" asked Harry.

"He's been a girl for three weeks," said Hermione. "The same girl."

"Well that's not too unusual," Harry replied. "That was the prediction, wasn't it? Once we had the ability to change our physical appearance at will, everyone made themselves pretty looking, but there was a treadmill effect, and so everyone made themselves even more pretty, until it was kind of ridiculous, and they all started looking the same anyway. The gorillas and rhinos and demon forms and what have you was the step after that, but I'd always said that eventually most people would settle into a standard form that they used the vast majority of the time."

"You said it would happen over the course of a few months," said Hermione. "And it's been years. And you know that Draco's never been much of a trendsetter. It's not in his blood. Even when he's a leader, he's still one that takes careful temperature of the people he's leading. And his girl form is just the tip of the iceberg. He's acting ... weird. Even by Hogwarts standards."

"Alright," said Harry. "I'll go find him and talk to him, if that's what you think needs doing."

Hermione nodded. "Thank you. And I'm going to add in an appointment for tomorrow, for us to talk about the secrecy statute. Draco has had enough votes to get it torn down for two months now. I'm not even saying that we need to tell the muggles anything about magic, just let them know that magic exists so we can stop forcibly removing their memories every time a dragon flies overhead."

"I suppose I'd be a fool not to have a reasoned discussion about it," said Harry. He kissed them both goodbye and headed off to Hogsmeade.

The fact that relationships at Hogwarts could now be better described by a cyclic graph than a list of pairs was not due to any real push by the Bayesian Cabal, but instead by Tracey Davis, who had worked out most of the theory behind it through a study of the mating habits of the witches, werewolves, and vampires that populated her favourite novels. She had thought it was her duty as a Silver Slytherin to put these theoretical concepts into practice, and had begun just as soon as she considered herself "old enough". Her way of structuring relationships had resulted in scandal, shock, disbelief, dismissal, a scrambling to accept the new order, and finally acceptance (Tracey Davis and the Double Witches). Having multiple partners was now simply The Way Hogwarts Was, much to the consternation of the Headmistress and many of the parents. Announcing that you were monogamous was usually met with a long pause, followed by, "... but why?" Harry and Hermione had talked it over for many months, but it was ultimately Draco that had decided things for them. He and Hermione had been spending a lot of time together working on a framework for keeping the muggle leaders in line, and they'd started to develop Feelings. A short couple of years later, and Harry was in a committed relationship with Hermione, Draco, Luna, and Bellatrix.

Draco lived near Hogsmeade, which was ten times larger than it had been when Harry had first come to Hogwarts. A small portion of the school had a tightly controlled hole in the anti-Apparation wards to allow visitors access to the Philosopher's Stone, and it was there that Harry headed. The Philosopher's Stone was always a hive of activity, with people rushing in and out to maximize the returns. If not for a strong Quietus Charm the air would have been thick with the sound of Apparation and Disapparation. The current safe limits on permanency were ten people at a time, all joined and linking hands, each transfigured using Partial Transfiguration - a secret that Harry had entrusted to the team of Aurors that kept the healing engine going night and day. If partial transfiguration could be used to explain to the magical interpretation engine that a metal ball wasn't a single object, then it could also be used to cheat and explain that ten people really were a single person. It had taken some testing to get this to work properly, but they'd been able to multiply the throughput enormously. The entire wizarding world, including all the non-human sentients that wanted it, had been through the Healing Room at Hogwarts in the first year. Now it was almost entirely muggles.

Harry watched the procession for a few minutes. They had run into some real personnel problems when it came to curing muggles, not least of which was the requirement to actually ask them instead of simply assuming that they wanted to be cured. Ten people every four minutes was all well and good, but those ten people had to be picked up from their hospitals, spoken to, transfigured, put under the stone, taken back to their hospital, and then memory sealed. Even with the systems they'd put in place, it was difficult to make full use of the stone - and the deaths that they were preventing sometimes seemed like they were overwhelmed by the sheer scale of the world population. There were other wizards who went to hospitals and handed out more simple magical cures, but wizarding labour was even more of a limiting factor there. There were one and a half million wizards and witches in the world, which simply wasn't enough, even if they were all devoted to doing good, which certainly wasn't the case. Yet at the same time, that large a number of wizards meant that it was likely that some monster or idiot would destroy the world. Adding more wizards, if such a thing could be done, would increase the ability to do good, but also increase existential risk.

Harry had to remind himself that the chime had sounded, and work was over for the day. Trying to do a risk-reward calculation now would defeat the entire purpose of downtime. He concentrated slightly, and apparated to Draco's house.

"You're here!" smiled Draco. She (and there was tremendous debate within Hogwarts about pronoun usage because of people like Draco who considered themselves one gender while outwardly wearing the other, and that wasn't even considering some of the new genders that had been introduced, or the people who were only sometimes genderless) was a tall, slender woman with white hair and a sly grin, most of her features suggestive of Malfoy's baseline male form. This wasn't a terribly uncommon thing to do. When you could be anyone you wanted to, trying out the opposite gender was one of the natural things to test out for a day. Draco was female more often than some others, especially when Harry was around.

Harry was pleasantly surprised when Draco wrapped her arms around him and drew him into a kiss. Of all his lovers, Draco was the one that he got to see the least, in large part because of the demands of both the Wizengamot and the International Confederation of Wizards. Draco lead the largest voting bloc in the Wizengamot, the so-called Nighttime Menagerie of young witches and wizards who had grown up under the Philosopher's Revolution (the first chapter of Draco Malfoy and the Nighttime Menagerie by Luna Lovegood had, due to a mixup, been published slightly before the events that it depicted, and so the name had been coined from nowhere). Amelia Bones was his primary opposition, and it had been no accident that their rivalry had realigned the axis of political debate within the wizarding world. Amelia Bones headed up the Homeguard, those witches and wizards who were more cautious about progress and all that it implied, though still devoted to good, and still with Harry Potter's ear. The photos of the Wizengamot run in The Daily Prophet often showed the white-haired, smirking Draco standing in front of his coterie of animals, spirits, goblins, beasts, and demons, with the grey-haired Amelia Bones and her aged conservatives frowning deeply at the opposition (though thanks to the Stone, their age was somewhere between a political statement and an affectation, rather than saying anything true about them).

"It's graduation day," said Harry with a smile when they broke their kiss.

Draco kept her arms around him. "I know," she replied. "The Silver Slytherins have a special party planned for just after midnight. We all passed our N.E.W.T.s ages ago, even Crabbe and Goyle, but ... there's something about having a way to mark the end of an era, you know?"

"I know," said Harry. "Listen, is there something that you need to tell me? Hermione said you'd been acting strangely, and Luna said that today was an important one, and I think that I can put two and two together."

"Ah," said Draco. She pulled away from him slightly and crossed her arms just below her breasts. "Well, the thing is ... do you recall what we did three weeks ago? You, and me, and Hermione?"

Harry smiled and nodded. "I was actually thinking that we should try that again. I know you and Luna aren't really in the same polyship, but the geometry might work out better with four, and ... well, my other partner is out for obvious reasons."

Draco shook her head. "I wasn't suggesting that we should do it again," she said slowly. "Though that would be lovely, I'm sure. But ... you were the only one with properly male anatomy, and I hadn't indulged with a man since then, and I know that we had precautions in place, but we must not have been careful enough - what I'm trying to say is that I'm pregnant." She looked at him carefully.

"Is that all?" asked Harry with a laugh. "Oh, I've known that was going to happen since I was thirteen. It was written in the Quibbler."

"YOU KNEW AND YOU DIDN'T TELL ME?!" asked Draco.

"I thought you knew!" cried Harry. "Am I really the only one that takes the Quibbler seriously?"

"But what are we going to do?" asked Draco.

"Well, Tracey Davis has some interesting ideas about how a plural wedding would work, and there was something else in the Quibbler that I saw so many years ago," Harry got to one knee, and quickly transfigured a ring with the Elder Wand. "Draco Malfoy, will you marry me? And keep in mind that you might cause a prophecy paradox if you say no."

Maybe it was the hormones, but Draco was crying. "Oh Harry, of course."