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He liked to watch them interact. They were normal teenagers, laughing and arguing with their friends. Of course, he wasn't among them.
From his first Sorting, he had concluded that the Hat wasn't the only one making the choice. So this time, instead of choosing Gryffindor over Slytherin, he asked for Hufflepuff over the two other Houses. Because Hufflepuffs, as loyal as they were, were always overlooked. And it suited his intents perfectly.
Day after day, he saw them growing up. He liked them as teenagers, he who had never got the chance to to know them as adults. Fiery Lily Evans was always ready to help a first year, prankster James Potter grew more responsible and kept the Marauders in line. Severus Snape, scowling, went to secret meetings to study potions with his only friend.
Because he liked watching them, so carefree, he got them rid of Peter. So the rat would never join his parents' murderer.
That's when the balance shifted.
To his displeasure, the atmosphere became tense after the corpse's recovery. The three remaining Marauders didn't play pranks anymore. Lily spent almost all of her time huddled together with Severus, somewhere. No one knew who had attacked the rat, naturally. Hufflepuffs weren't high on the suspects' list, in these times of war. It just bothered him that now people would forever see the traitor as a martyr on Light's side.
The sooner it would be all over, the sooner he would see them all smile again. And so, although it would be quite hard to do under Dumbledore's watchful eyes, he would track down the Death Eaters.
He did so, and stumbled upon an unexpected ally on his way back from hexing Lucius Malefoy.
Namely a young Madam Malefoy.
Formerly Narcissa Black.
Married to Lucius because that is what pureblood families live on : arranged betrothals and inbreeding. And so she helped him.
The final battle was almost a perfect replica of the first one in his past. Or in the future, whichever. Because, he figured, if he had already changed his future so much, it didn't matter what he called it. If he killed just one more time, he would ensure Lily and James's happiness.
Even if he were to kill Voldemort a second time.
They were all there to help him. Narcissa, of course, but also James, Lily, Remus, Sirius, Order members and even Severus. In front of them, the remnants of the Dark Lord's followers, and a livid Tom Marvolo Riddle, eyes flashing red in fury. The same as last time.
Wands were drawn, curses shot, beams of light cast strange shadows on the fighters' faces. Voldemort died by his hand again, the battle stopped as quickly as it had begun. People fled. The ''Light'' side rejoiced.
And Lily Evans glanced at Severus Snape, quickly, before averting her eyes.
And James Potter smiled shyly at Narcissa Black.
And Harry Potter disappeared, just like that, because he was never to be born.