It was an accident.
The stove hadn't been left burning on purpose, Harry hadn't stayed out at the park for so long on purpose, and the Dursleys hadn't been killed on purpose.
Probably.
He could ignore the reverberating knowledge that, even if not planned outright, he knew fire safety and knew that he had turned a blind eye to the burner he had left on when he left the house.
The day was the same as any other. The Dursleys were in bad moods, it was slightly foggy, and Harry was doing his best to be unseen, unheard, and unacknowledged.
And then he found a lighter on the ground while walking to the grocery store.
It was small, had a plastic green exterior, and looked half-full of lighter fluid. Harry had only noticed it because he tripped on it, and even then he barely paid it any mind.
Still, though, if the Dursleys followed through on their promise to kick him out as soon as he turned 18, or any of their other threats, a potential weapon and tool would be useful.
So, he picked the lighter up and stuffed it into a pocket. It had already been left by whoever had owned it before him, so he didn't have to worry about the morality of theft, and it would be easy to hide so he didn't have to worry about the Dursleys shipping him off to a psych ward or prison for plotting to set them all on fire and/or commit arson.
And just like that, he went about his day and completely forgot about the little green lighter after he had hidden it.
At first, he just turns the wheel of the lighter to see how it works.
Then, it's a comforting habit.
And now, it's to see the little spark, the flickering red fire, to feel the heat near his thumb that's not hurting him but is noticeable at the edges of his senses.
The sound of the metal, the wisps of heat from the fire, and the weight of the lighter all become sensations that put him at ease as soon as he experiences them.
It's only natural that he progresses to the next logical step; a bigger fire.
There's a clearing in the woods next to the park with a little circle of stones and stray bricks making up a firepit, and with school over for the summer, Harry has plenty of time to find it and make sure that any fires he starts won't spread.
The smoke rising from the trees is never noticed or reported.
As the weeks pass and his fires get bigger, Harry gets bolder.
He doesn't stay so far from the bright, overwhelmingly warm fires he starts. He gets closer and closer, until it's just this side of uncomfortable and if he came any closer he'd need medical attention.
He leaves more kindling in the pit before bringing out one of the lighters he's stolen and watching as the fire builds, the animals go further into the forest, and smoke fills the air and makes his eyes burn.
He spends less and less time with the Dursleys, leaving at dawn and returning long past dusk.
The most noticeable thing, perhaps, is the stray trash that he nudges into the fire to watch melt, burn, or explode, in the case of the alcohol left behind by a group of teenagers he had found.
The explosion had been small, but all the more devastating for its beauty.
Eventually, dead things start making it into the pit.
They're already dead, so it's not harming them.
People get burnt after dying, so how are animals any different?
Soon, the fires are all he thinks about.
He looks at the stove every time he passes through the kitchen, keeps an eye out for lost lighters on the sidewalk, and whenever he closes his eyes he sees the explosion the alcohol had caused.
He knows that his fires have gotten as big and bright as they can safely be, but he can't help but wish for more.
The housefire probably hadn't been an accident, had it?
The Dursleys had been oh-so-vocal about how worthless and pathetic he was, all of the wood he usually used as kindling was wet from the rain last night, and he had been in the kitchen to cook breakfast.
He had been the last one in the kitchen.
He had been the one who left the stove on.
He had been the only one who left the house, even though everything outside was damp and cold.
And, well, he had entertained dragging Dudley to a bonfire and seeing how big of a fire he could become.
Looking at the house, seeing the fire licking at the windows and exploding from the doors, and hearing frantic screams, he can't say he regrets it.
He can't regret something with such pretty hues and unbiased destruction. Rather, he lingers to see the blues, reds, and faint whites eating away at the house's siding and listens as the screams die down and firefighters arrive.
And for the life of him, he can't help but hope that the next fire is bigger.