DISCLAIMER: Harry Potter belongs to J.K. Rowling, who isn't me. The only profit I get from this is personal satisfaction.
George Weasley and the Computational Error
George Weasley had a shadow over his soul ever since he lost his brother, Fred. He had tried to live for both himself and his identical twin that fateful day, but he always knew it could never be enough.
His son, Fred Jr, had always tried to live up to the elder twin's memory, but the pranking gene had skipped a generation, it seemed. Fred (although Angelina always called him Junior, George had insisted on using Fred's name whenever he could so that he—for that fraction of a moment—could pretend his brother was alive once more) had deplorable attempts at creating mischief, despite growing up in the most successful prank shop in Britain. It was probably just too much pressure on the boy and not enough true release into the realm of fun. George simply wasn't a good example of that free whimsy anymore—Ron of all people was the one who usually came up with new ideas for products while George applied his years of knowledge to make them real. And tomorrow he and his sister would start Hogwarts.
George waited until Angelina fell asleep before he got up and took his broom out for a ride. It emptied his head so that he didn't have to deal with the nightmares about his twin dying over and over again. Too much, anyway. Every birthday, Christmas, anniversary—and now the first day of school—the nightmares would come even if he took a Dreamless Sleep Potion.
As he flew, he became aware of a small globe of light that seemed to be following him. George tried to shake it off, but it was more determined than a Bludger under the influence of a maiming house-elf.
"Wait up!" a voice said from behind him. "I just want to talk!"
George slowed his broom, but kept a wand in one hand and his other in his pocket, where he kept his Peruvian Instant Darkness Powder.
"Thank you," the voice, emanating from the sphere of light, said. "I have something rather important to talk to you about."
"Couldn't you have waited until the shop opened?" George asked.
"No. I am making a proposition."
"And I am happily married, thank you. And I have no idea whether you're female or not, as you sound rather androgynous—not that it matters."
"It doesn't," the voice agreed. "I was talking more along the lines of me offering you an opportunity I know you won't refuse."
"And what is that?" George asked.
"A chance to save Fred."
"What have you done with my son?" George asked, gripping his wand tighter.
"Nothing at all—and I'm not going to. I was talking about your son's namesake."
George scoffed. "Fred is dead—barring time travel, I'm not going to save him from anything anytime soon."
"Good, because that was exactly what I had in mind."
George's broom fell a couple feet before he regained enough control over his brain to catch himself. This little orb of light was definitely controlled by a malicious prankster. "Are Harry and all of his friends coming too?" he deadpanned.
"I can't send anyone else back because the universe would notice an extra version of themselves running around for an extended period of time and it would try to correct it. You, however, already have a duplicate that the universe knows about and it would just assume that it's you're a computational error and not a problem. The Creator is quite bad with numbers, you see, and the universe has learned to compensate. You can exploit this."
"So you're going to send my spirit back to the Battle of Hogwarts so I can save Fred, is that it?" George asked.
"No, it'll have to be your whole body as it is currently," the voice replied. "Where did you get the idea that time travel didn't involve moving matter?"
"Do you have any idea how many of my nieces and nephews have written stories about how one of their relatives or family friends have gone back in time to relive their years at Hogwarts?" George asked. "That sort of thing isn't going to work if they are still their older selves, physically speaking."
"Okay," the voice said, "I'm not sure if I should tell you this, but I think it may be possible for you to do things your way, but that means that you'll have to go back to first year—before most people notice a change in you—instead of just before the Battle of Hogwarts."
"What do I do?" Even if this was some bizarre prank, George couldn't let an opportunity like this one fly away from him.
"You'll have to sporadically possess your younger self," the voice explained. "You can't do it continuously or your current body will die and the universe will realize something is wrong. I think I can add the conditions to the mechanism that'll send you back, so you have nothing to worry about."
"What about limitations?"
"You only get to go back once, but once you're there, you're free to alter history as much as you want. I'd advise you to keep your current body from being very close to Fred's for very long, at least for a few years, so the universe doesn't look at you too closely. At the very least, keep the fact that you're a time traveler in your head for at least one year—after that, you're more or less integrated into that version of the universe and it's much more difficult for you to be deleted, although it's highly advisable to wait—just in case."
"And just what do you get out of all this?"
"I just want to swindle the universe. Surely you can understand that?"
"I suppose I do," George laughed. "When can I go back?"
"Don't you want to say goodbye to all of your loved ones first?"
"Why?" George asked. "This timeline won't have existed after I go."
"You don't know that. For all you know, this reality will continue and it'll be like you died and your body was lost in Majorca, never to be found."
"Obscure reference, never mind."
"As much as I love my family here, I'd give anything to see Fred alive again."
"Normal people invest in a Pensieve," the voice said dryly. "But, of course, we are not normal. We strive for insanity and hope we kill Dark Lords on the way."
"You want me to use my future knowledge to kill He Who Must Not Be Nosed?"
"I'd make sure I got the full details from Ron or Harry before I tried anything that stupid, if I were you. You're just going back to make sure that a certain wall doesn't explode while Fred is under it. Of course, the likelihood of that exact incident happening again after you spend nine years destroying the timeline is pretty slim."
"You want me to preserve the timeline, don't you?"
"They call me 'the Trickster' for a reason: you'll never know what type of gambit I'm trying to pull, but it's going to be hunky dory by the end of it."
George decided to just leave a note for everyone—he had more relatives than he could count after all—but he gave personal goodbyes to Angelina, Fred, and Roxanne. He didn't tell them where he really was going, but he made it clear that he would probably only come back "if the universe spits him back out."
He kicked his broom up into the air and the light globe returned. "You've been crying, haven't you?"
"You tell your family 'goodbye forever' and try not to cry," George retorted.
"Has your decision changed?" the voice asked.
"No. Fred is Fred. I'm not going to abandon him again."
"I can leech out the potency of their memories for you," the voice offered.
George considered it. "I'll still remember them, right?"
"Yes, but you won't miss them and you can focus on your brother without worrying about this timeline. If here continues to exist, I'll make sure they're okay when you're gone."
George nodded. "Do it."
"Close your eyes and focus your mind on the ones you love. Focus." George felt a tickling sensation on the side of his head. "It is done. Are you ready to return to 1989?"
"Keep your eyes closed." George felt a chain being placed around his neck, followed by a small prick on his arm and the sensation of his head being submerged in water. Then things proceeded to get so fast and weird that he doubted that he'd be able to remember it all without assistance from a Pensieve. Still, George decided figuring out the secret behind time travel was useful enough knowledge that he'd have to sneak into Dumbledore's office and borrow his Pensieve sometime.
Suddenly, George felt different—the time travel was successful.