Yes, a Harry Potter sorted into Slytherin, a Harry Potter who - angry at his treatment by his aunt and uncle - used his magic in the days before his letter, to torment Dudley. A Harry Potter with a personality making him a dark lord in the making.
I can see it now: he hears about the Philosopher's Stone and wants it for himself. He rejects Voldy's offer not out of being good, but instead sneers at Voldemort, saying, "You are a weak, washed up excuse for a wizard, Voldemort. You have no body, you have no powers. Your time has passed." I don't know whether to let evil Harry have the stone or not. But... maybe despite being in Slytherin, he fools Dumbledore into thinking he's good. No, I've got it: Harry keeps the stone and claims Voldemort and Quirrel took off with it (by killing Quirrel and transfiguring Quirrel's dead body into a book or something). How things will go later when Voldemort still has not used it to return to his body, I don't know. Maybe Dumbledore even gets suspicious.
Ron and Harry not friends; Harry's best friend is Draco Malfoy, instead. Because instead of turning down Malfoy's hand, he took it. Crabbe and Goyle are their thugs. Harry becomes Slytherin seeker in his second year.
Then, for the second book, when he finds out he's a parselmouth, he quickly realizes he's hearing a snake in the pipes. He asks the librarian about magical creatures that are snakes, and she tells him about Basilisks. He then hunts down the culprit; he steals the diary from Ginny without her knowing, and - not knowing what it is but suspecting its power - either hides the book, or demands Tom Riddle tell him where the Basilisk is. Tom does not cooperate, so Harry hides the diary somewhere other than his bedroom until he can figure out what to do with it. He isn't ready to use the Basilisk himself, so he leaves it be.
Wait, no... that's boring. Better have, instead, the same kind of fight between Harry and Tom as before, but Harry has read up on curses and uses Imperious on the Basilisk, commanding it to sink a fang into the diary, killing the diary. He then commands the Basilisk to retreat before Ginny wakes up. Spins a tale for Dumbledore, is seen as the hero again. But his secret Slytherin family knows something of the truth, if not the whole truth.
For the third book, stuff happens pretty much as normal. Everyone hated Lockhart, so he gets sacked and replaced by Lupin. Harry quickly figures out Lupin's secret, keeps the secret to himself while he figures out how to use Lupin. Sirius Black tries to go after Pettigrew again, confuses people by going for Gryffindor when Harry is in Slytherin.
Harry is curious about Sirius Black. Finds out he supposedly got Harry's parents killed; this doesn't bother Harry for the same reasons, as he never knew his parents. But he's angry that Black is the reason he had to go live with muggles. Somehow Harry gets down to the Shrieking Shack and disarms Black. Tells Black it's his fault that Harry had to live with the Dursleys, stuns Black as he's trying to tell the truth. Helps Ron get back even though they're enemies, Sirius is turned over to the Dementors, Scabbers remains with Ron. Possibly have Lupin and Snape involved still, somehow. I don't know the details. Trelawney still makes her prediction. Or perhaps have something else happen that causes Scabbers to run away. Maybe he's trying to get away from Crookshanks.
I don't know how to do the fourth book. Though maybe similar to normal, at first. Draco Malfoy being rich, he has his father extend an invitation to him to join them at the Quidditch World Cup. Draco has told his father everything about Harry, so Lucius is a fan. Possibly even switching allegances to follow Harry. Everything else goes fairly the same as in the canon book, but Harry does better at the tournament and he doesn't bother helping Cedric when imperioused Crum attacks him. Goes to the graveyard by himself, but is instantly wary. The whole "scar prickling" thing doesn't happen in this series because it only happened in canon due to Harry being so loving. So he's not debilitated by any scar pain when Wormtail apears. He kills Wormtail, Nagini, and then makes a portkey to send the weakened Voldemort into the ocean. Returns as though nothing has happened. Figures out who the traitor was, unmasks the fake Moody, hands him over to Dumbledore.
Without Voldy being back, the fifth book has no Umbridge or Ministry interference. So we could literally do anything with that. Probably have Harry start making new plans, which include finding out why that annoying vermin Voldemort is still alive. He possibly even asks Snape, who is a friend, for help. Snape, who still wants Voldemort dead for good because he'd been in love with Lily, is still working with Dumbledore even though he's now a triple agent, because his true allegiance is with Harry. Anyway, Snape demands answers from Dumbledore, but doesn't get them. So he does some digging outside school for Harry and finds it. Everything about the horcruxes, one book early. The only piece they're missing is how many Horcruxes there are. They know there's got to be at least two, since they've figured out that the diary was one. The Basilisk is still down there, alive, so they have a way of destroying the others when they find them. Don't know who the DADA teacher would be in this one, but NOT Snape or Umbridge.
Sixth book, Horace Slughorn is the new DADA teacher. Snape finds out that Slughorn once taught young Tom Riddle, suspects there may be an important clue about the horcruxes there. Uses the Imperious curse and Veritaserum to get the truth out of Slughorn. He and Harry then have the missing piece of the puzzle: six horcruxes. Though they eventually figure out Voldy never got a chance to make a sixth. As far as he knew, anyway.
Of course, Dumbledore is working on that angle too, and Snape is called to help Dumbledore after foolishly trying to use the resurrection stone, as before. Since Voldy is still weak and pitiful, no need for Snape to murder Dumbledore. But Dumbledore dies anyway. Evil Harry is glad, for the same reason Voldemort would be.
Throughout the sixth book, Snape and Harry and Dumbledore find more horcruxes and destroy them. Having never been in Sirius's house, since Sirius got soul-sucked in the third book, they don't know about Regulus's locket at first. But after a while, Snape gets a brainwave; he figures out R.A.B. because he knew Regulus in their Death Eater days, so at some point they visit his old house and get the truth from Kreacher. They retrieve the locket, use the Basilisk against it.
Not sure how they would find the cup. I mean, with Dumbledore still working with them, they know about the cup, but they don't know where it is. Nor do they know about the Diadem. They guess about the Diadem, after Snape uses some excuse to get into Ravenclaw tower and look for possibilities. Also Draco had, for some reason, wandered into the Room of Lost Things and remembered seeing a crown, so they go after it, verify it's a horcrux, and destroy it.
In the seventh book, there's just the cup left to find. Harry continues his plans for gaining power as well. He has gathered old Death Eaters into his army, he is now the new Dark Lord around which they rally. Voldemort, still less than a ghost, is pissed but can't do anything about it. Harry tells his new servants, among whom is Bellatrix Lestrange, about Voldemort's horcruxes, and she knows where the cup is. She retrieves it for her new master, it is destroyed. But reports return that ghostly Voldy is still persisting. So Snape, still playing Dumbledore's pet, asks Dumbledore's portrait about it. Thanks to some careful Imperious curses, the portrait hasn't heard the whispers of Harry's rise to power, so he tells Snape that Harry is likely the last Horcrux, and Voldemort must kill him. This goes over about as well as you might expect, and Harry decides ghostly Voldy isn't worth the risk, orders some of his servants to keep an eye on Voldy.
But Harry's servants are no longer Death Eaters. They are now called Death Golems. Harry is going by a new name as well, Lord Harry Sarpati. The new Dark Lord takes over the Ministry and Hogwarts, with Snape as headmaster. Voldemort still powerless, Snape returns to his evil ways under Lord Harry. A resistance builds up, led by Neville Longbottom. Knowing about the Room of Requirement from Draco, Lord Harry kidnaps one of the resistence and tortures him/her until they tell how to get into the room under its new management. Imperiouses that person, sends him to rejoin the resistence, claiming he was never captured. Then one night, the Imperioused person lets the door open and Lord Harry sends the basilisk in to kill everyone in the room, but Neville escapes.
Lord Harry can now begin his own experiments in invincibility. He wants something different from horcruxes, though; he doesn't want to become a weak and pathetic worse-than-ghost like Riddle did. He also researches a way to destroy the last horcrux without killing himself. And one thing he does find is how to bind Voldemort's last remaining free-floating soul piece to its own horcrux, effectively imprisoning Voldy until Harry can figure out a more permanent solution.
Lord Harry is a different evil overlord than Voldemort. He doesn't care so much about heritage, so doesn't target anyone magical unless they resist him. He breaks the international statute of secrecy, turning Britain into his own private slave state. Muggles are enslaved, wizards and witches must join him or die. Other muggle countries try to fight Lord Harry's Britain, to no avail. The Dursleys and Aunt Marge were the first to die, Lord Harry did those murders himself.
Lord Harry spreads his reign of terror into mainland Europe, sending vampires and werewolves after resistence leaders. In a few short years, he has conquered most of Europe.
He explores the world looking for magical information while his forces back home fight his war for him. He finds out how to rid himself of Voldemort forevermore, by forcing the errant soul-piece out of his own body and into the same horcrux he's trapped Voldy in. Then just one bite from the basilisk, and no more Voldemort.
Eventually, Neville Longbottom manages to kill Lord Harry before Harry found out how to become invincible. His refusal to use horcruxes, even though he had the philosopher's stone, killed him in the end. But the secret is out, and the world will never be the same. It looks like the war between wizards and muggles is only beginning.
This was cross-posted from http://fayanora.dreamwidth.org/1159781.html
You can comment either here or there.