(Harry Potter is a squib. He lost his magic on Halloween 1981, when something dark and greedy latched onto his soul and fed from him.)
When Dumbledore inspects him on the night that he is delivered to the Dursleys, he finds that in the grand scheme of things, a little magic is nothing. A little magic will keep a soul shard suffocated and trapped.
Lily Potter was not the only sacrifice made that night. As quickly as owls can possibly fly, it comes around in whispers that the Boy-Who-Lived died days later.
The wizarding world mourns, of course. They make shrines and sing odes. But nothing, not even a death can keep the defeat of Voldemort depressing for long, and soon they raise glasses to him in his honor again.
("For Harry Potter, the babe who faced Voldemort and lived to tell the tale!"
"Aye!," a rousing cheer comes from the drunks. Some of the more coherent patrons frown.)
We're getting ahead of ourselves here.
On November 1st, Petunia finds a letter on her doorstep along with a screaming, bawling, green-eyed infant.
Petunia takes him in. She reads the letter, and then looks over at the baby whom she has placed on the sofa. She knows what to expect to see, even though she has never visited her sister after the birth. Eyes that are green(Lily), which is a color she hates. Freakish, unnatural eyes.
The baby's eyes are a murky green. The color isn't even visible unless in direct light. Petunia looks at him, and f̶e̶e̶l̶s̶ a̶ k̶i̶n̶s̶h̶i̶p̶ takes in an orphan.
Harry Potter does not have a good childhood, but it's not as bad as it could have been.
He's given food, clothes that fit and a room upstairs. Vernon Dursley still 'kept him in line' in the way he himself was brought up, because unlike his son, his nephew is a quiet, stricken child.
Harry dreams of green light and flying motorbikes, and wakes up alone, screaming into the sheets. He dreams of strange animals, the most recognizable of which is a shaggy dog.
On one of her visits, Marge sets Ripper on Harry. The dog snaps at him and then rolls over and lolls its tongue out. Harry, it seems, has a knack with dogs. Dudley tries to hide his panic.
Years pass. Dudley's 11th birthday arrives, Harry wakes up early to tidy out his room. There are pictures of his parents on his bed stand and even with the amounts of candy Dudley tries to stash in there, it is a pretty good room. He does some assigned reading, then remembers what day it is and heads downstairs.
Vernon is already on the couch, furiously wrestling with the wrapping paper on one of the boxes. The rest lay around him in a colorful pile. Harry remembered that Vernon thought that he was a waste of space and a drain on their money, but all of this had been said to Petunia at night when he and Dudley ought to have been asleep and also Harry didn't care.
"Uncle Vernon, should I wrap some?" he asks, just to be on the safe side.
Vernon glares at him, and sends him off to the kitchen, to 'do something useful'
Petunia asks if he shouldn't be doing his homework, but sets him to cutting up vegetables anyway. She's making a huge delicious fry-up, and asks Harry about how Dudley is doing at school while she cooks.
By the time Dudley comes downstairs, breakfast is done, and he is given a ludicrous amount of presents. The rest of the day passes quickly, with the birthday party, massive amounts of cake and a pinata shaped like a video game character. They went to the zoo, where Dudley and Harry had great fun watching a snake sleep and speculating to each other how they could get it to eat Mrs. Nikol, a teacher at the local primary.
[Dudley Dursley is spoiled rotten by his parents, and doesn't know what to make of the new stranger.
Harry is something his mother doesn't have an opinion on, but whom she looks sorry for. Still, Harry is the one who will play with him when Petunia keeps him inside, who shows him animals are unthreatening if treated right. He's the one who faces down Ripper and stops him from taking a chunk out of Dudley's leg before Marge can intervene.
Harry is Dudley's brother, in all the ways that matter.]