He couldn't do it. He thought he could at first but putting up with child abuse is never easy, even when you've got an older bloke's memories crammed into your head.
So one day Harry Potter simply left. It was either that or wait until they either killed him or he was forced to defend himself with magic making things even harder on him after.
He didn't dare go to Diagon Alley despite wanting desperately to start learning magic. Sure, he bleached his hair and wore a cap, but Dumbledore surely would find out soon enough he left and he didn't want to be returned to them.
He knew he shouldn't have left as soon as he did it, but emotions and impulse control aren't just mental- the brain doesn't fully develop until your mid twenties they say, and before that and even after you're at the mercy of your brain's chemistry.
Still, he couldn't just go back to them- Harry of canon had survived but that was no guarantee he would- and he just couldn't take anymore of it. He'd take his chances of death eaters finding him over the Dursley's neglect and outright abuse any day.
Shifting the pilfered backpack on his shoulders he kept walking aimlessly through the streets trying to get as much distance as he could from the Dursley's house.
He had little choice but to run on a weekday- they paid far too much attention to him on weekends and like hell was he waiting till Summer vacation, so he wasn't surprised a few hours in as the Sun was nearly at it's peak that the cop spotted him. "Shouldn't you be in school?"
He shrugged, "I'm home schooled." He muttered, and kept walking. Unsurprising the cop did not like that and he felt himself grabbed by the shoulder and knew it was next to hopeless to get away, though given his plan had been to get as far away before getting caught as a runaway, that was fine.
No matter what the cop or the social worker said he gave no real details- So what if they didn't have a record of a Martin Greenwood? So what if they didn't believe him when he said he didn't know his address but was 'pretty sure it's in Dover', he didn't give anything away no matter the threats or pleas.
The orphanage was infinitely better than the Dursley's house. Sure, the servings were small... compared to what a kid in a normal home got, but compared to the Dursley's leavings? He ate like a king.
So what if the other kids didn't like him thinking him a swot because he liked to read and wanted as little to do with the snot nosed brats as he could? It wasn't like they could really do anything about it.
At least, that's what he thought, the insults had barely so much as stung, but the violence was unexpected.
The thing about fighting kids is pain tolerance- he had it in spades even without having experience of a handful of fights and injuries in his previous life, he had plenty in this life.
It made him sick to his stomach hurting children, but he hardly wanted to be in pain. He noticed it getting easier to bare which worried him and gave him nightmares at first, but... he started enjoying it more and more, and he dealt greater and greater pain to those that attempted to torment him, eventually adding in his wandless magic which was improving in unexpected leaps of bounds.
He started worrying significantly less, he was doing what he had to, right?
Even the dreams weren't something he was bothered much by- weird though they were he was already having dreams featuring his new body and old and combinations of the two, dreams of being some other kid in a different orphanage were weird but not shocking.
He figured it out one morning he had been combing his unruly hair and the Matron shouted "Time for church! Hurry up boy, you need it more than most!" His anger at being called boy and forced to attend something he didn't believe in flared and the mirror cracked from accidental magic drawing his eyes to it. He nearly screamed as he saw they were red, not as if irritated, but a deep glowing crimson.
He realized what had been happening, and was horrified.
He considered, going back to the Dursleys- maybe it would help, those blood wards- perhaps were the only thing preventing just this from happening- but the mere thought sent agony through his skull.
The thought of telling Dumbledore elicited if anything a worse reaction, his head feeling like it was being torn apart, making his nose and ears bleed alarmingly.
As time went on thoughts of salvation lessened even as he grew colder and meaner.
He was horrified how much he enjoyed it, hurting those beneath him, who dared wrong him, but he saw no way out but one. The mere idea had him convulsing on the floor silently screaming his agony, as even the option of suicide was rendered unthinkable.
The feelings that it was wrong got smaller day after and day, and eventually he stopped worrying about it at all.
It wasn't hard to switch out the stone with a fake, Hagrid wasn't the brightest of beings, then he took him back to the Dursley's house. Any guilt Harry felt about stealing the stone died with Hagrid's treachery. There was a house fire, very tragic. The Weasley's were even better than the orphanage; marginally.
When Harry Potter came to Hogwarts he'd be seen as a charming intelligent young man with a bright future ahead of him. His sorting had only caused minor controversy, but Ravenclaw was a perfectly respectable house. It had only taken a minor threat to get the hat to comply.
He was so polite and helpful to those around him and well liked that any worry's about the odd sorting were forgotten. Only Snape seemed to be against him but even so he backed down over the threat he hanged over the man's neck, "You like calling me a celebrity, so I shall use it. Leave me be or the Daily Prophet shall get an interview on just who lead Voldemort my parents to their death." The mixture of shock and horror on the man's face was like a fine wine.
"We are so alike, you and I. Both half-bloods that grew up in orphanages hating our muggle caretakers... Like me there is a potential for greatness... Join me and we will be unstoppable."
Harry chuckled "Sure, put her there!" He held out his hand and reluctantly Quirrell's hand reached out. And there was fire. "Join you? Ha, that's a laugh." The shock and outrage plainly on his mutated face was wonderful, Harry thought, even as it morphed into pain and horror as his struggles to wrench his arm free were met with resistance. Harry grinned, it had been worth it to figure out how to use magic for body enhancement, and fire manipulation.
"Your Mother's love Harry, that's what stopped him! Do not feel guilty for it, for he surely would have killed you and many more besides." Dumbledore said firmly.
Harry tried for a weak smile as if he didn't fully believe him but was trying, and Dumbledore left relieved that Harry would be alright, as soon as the old fool was gone Harry's eyes flashed crimson.