Au where petunia is a witch and lily is a muggle?
When the letter arrives, Lily is almost as excited as Petunia. She writes Albus Dumbledore to ask if she can go to, and if she cries a little when the answer comes back no she doesn’t tell anyone. Lily waves from the train platform, writes diligently, and listens with excitement whenever her big sister deigns to share stories of magic.
Petunia gets Sorted Slytherin, where she falls into a mutually-venemous friendship with Severus Snape, who she had considered dirty and poor when he was skulking around Lily in their little neighborhood, lighting leaves on fire like a baby arsonist, but who now seems like the best ally in a pool of ugly little fish.
The blood-purists are their normal asshole selves, which Petunia responds to with busybody eavesdropping, cruel gossip, and manipulative emotional bullying. Severus calls her mudblood in their fifth year (it’s not the first time) and joins the Death Eaters. Tuney calls him a greasy git of a wanker and they still have lunch away from prying eyes now and then.
When the war comes, Petunia does not fight in it. She marries a Hufflepuff boy named Vincent Dunsley who spends their entire first date telling her about his junior position in the Ministry and his planned thirty-six bureaucratic steps to the top of the food chain. Vincent has no problem with Muggleborns, or at least not ones who behave as properly as Petunia.
Lily does fight. She’s been reading the Daily Prophet for years as she sits through history class dreaming of brooms and punching bullies on the playground. At seventeen, she writes Albus Dumbledore again. When he still writes back no, she packs a bag and shows up on the Order’s doorstep.
Alice Longbottom gives her a place to stay, some spare robes, and teaches her how to fly– Lily hopes, wrapped in a warm blanket while they sip cocoa and discuss action plans, that if she’d gone to Hogwarts she’d have been good enough to get Sorted Hufflepuff. Frank beams at his wife in the dim yellow light.
Of the Marauders, Lily meets Sirius first– shaggy hair and strong bones, he’s a tall glass of water and he’s anxiously watching a skinny, scarred boy sleep on the sofa. They’re an hour off a mission and Remus crashed as soon as they got back to headquarters. The first thing Sirius Black, troublemaker and risktaker, says to her is “Shh! You walk like an elephant.”
She’d snap back, but Remus does look that worn down, curled on the cushions.
Peter and James are in the kitchen, shoveling sandwiches down their gullets that are the size of their heads. James staggers to his feet when she comes in. “Hi. Uh, new recruit?”
“Something like that.”
James shoves his hair out of his eyes with one hand and thrusts the other one out in her direction. “James Potter,” he says. “Beauxbatons? I don’t think I ever saw you at Hogwarts.”
She grins. “Lily Evans,” she says. “Cokeworth. And I’d shake your hand, but you’ve got mustard on it.”
Lily defies the Dark Lord and his forces three times, with James’s wand at her back, with Remus’s and Sirius’s and Peter’s. They tell her about Hogwarts and its secrets, and she brings them Muggle candy bars and the boxes of X-Men comic books from under her bed. No one gets chocolate smudges on her pages, under threat of James’s disappointed-in-you face, which he’s been practicing.
Severus Snape hears about a Muggle Evans on the warfront. “Petunia’s not a Muggle,” he snaps when Dolohov mocks him for it, but Crabbe cradles his broken arm and keeps talking– about green eyes, red hair like a war banner– and Severus’s stomach sinks low in his gut, cold and aching.
Severus Snape overhears a prophecy and he tells it to his Lord. Lily Evans Potter is the mother of a halfblood boy with a mess of dark hair. Lily is in Augusta Longbottom’s living room, playing peekaboo with Harry and Neville, because Alice and Frank are already in St. Mungo’s, because she does not know that she is soon to be not a soldier but a fugitive. Her child has no scars, yet.
On Halloween night 1981, Tom Riddle goes to the Godric’s Hollow home that Peter Pettigrew betrayed. He kills James in the front room, wand in hand. He kills Lily in the nursery, after giving her a chance to step aside. He tries to kill Harry, but he fails.
Harry goes to his closest living relatives– his aunt Petunia, uncle Vincent, and cousin Dudley. He sleeps in a little room just off the kitchen, which he thinks used to be a broom closet. They hate the attention he brings when he’s dragged behind his aunt at the grocery store, so they leave Harry home when they go to Diagon Alley, Ministry potlucks, or the evening shows that Dudley fusses through, fists full of pumpkin pasties.
Harry knows how to wash dishes by hand, how to cook bacon without burning it (most mornings), and how to capture the spiders in the broom closet and escort them carefully outside. For his birthday Dudley gets a toy broom. For his, Harry gets an Albus Dumbledore Chocolate Frog card because Dudley already has fifteen and didn’t want that one. Petunia likes to peer over the hedge into the yard of Mrs. Figg, the squib who lives next door, and snigger about how she has to do her laundry without magic.
When Harry is ten years old, his Hogwarts letter comes in the mail and the Dunsleys are surprised. “I wasn’t sure,” Petunia sniffs. “I mean, with my sister’s blood in you and everything, anything could have happened.”