Harry really could share his magic with others through a contract.
The Sorcerer Supreme had called this ability "lending"—a power unique to dimensional demon gods.
The chaos magic in Harry's body was extraordinarily special, first and foremost in sheer quantity.
According to the Sorcerer Supreme, Harry's chaos magic already exceeded the total power of some weaker dimensions—and was still growing exponentially every passing moment.
If Harry could perfectly control that magic, he could easily destroy planets and become the strongest Sorcerer Supreme in history.
But chaos magic was, by its very nature, chaotic and unordered. In that other world, any time Harry dared to use more power than he could firmly control, his magic would spiral out of control and cause irreversible devastation to everything around him.
Once, the Sorcerer Supreme had taken Harry to a hell dimension. When he fully unleashed his power there, he'd nearly torn that entire dimension apart.
Because of how unstable his power was, there were many spells he simply couldn't use in that world—and lending was one of them.
No one knew when his magic might slip its leash. If it happened while he was lending power, the borrower could suddenly be flooded with an ocean of chaos magic their body couldn't withstand. They'd explode like an overinflated balloon.
But in this world, although the amount of magic he could actively access had decreased, his control over it had improved tremendously. It was almost impossible for it to go out of control.
So after some research, he'd finally become able to lend his magic to others.
And Aunt Petunia, who had always secretly longed for magic, was going to be his first borrower. Not only would that make up for her old regrets, it would also let Harry "reasonably" get back at the Dursleys.
The mischievous smile on his face only grew.
"Remember this, all right?" Harry said. "In the world of magic, the basic principle is equivalent exchange. If you borrow my power, you have to pay a price.
"So—do you want to borrow it? Do you want to become sorcerers?"
The Dursley family stared blankly at Harry's smiling, boyish face. It was the same face he'd always had, but there was no trace of the old timidness left—only a deep, cold malice.
It felt like they were signing a contract with the Devil. Even knowing they might have to pay with their souls, they still couldn't push down their greed.
Gulp.
Aunt Petunia swallowed hard. She stared at her nephew—familiar yet suddenly so foreign—and asked in a trembling voice:
"What… what price do we have to pay?"
Harry thought for a moment, then replied,
"Well, since you're family, I'll give you a special discount—one percent off. Ten pounds for each use of a low-level spell, one thousand pounds for a mid-level spell, ten thousand pounds for a high-level spell.
"You can also buy permanent usage rights for a spell outright. That costs a thousand times the normal price.
"Oh, and after casting, you have to shout 'I'm an idiot.' That's the casting cost."
Petunia and Vernon glanced at each other, confused.
"That's it?" Petunia asked. "No soul, no lifespan, nothing like that?"
Harry rolled his eyes.
"What would I even do with your souls? How much could those possibly be worth? It's not like I'm a Dark wizard.
"Of course, if you insist on paying with souls, that's not impossible either. I've got a complete transaction system—absolutely fair to everyone.
"Since you're my family, each of your souls can be exchanged for the permanent usage rights of one high-level spell."
"Permanent rights to one spell…" Petunia murmured, immediately doing the math. "A high-level spell is ten thousand pounds per use, so a thousand times that is ten million pounds. My goodness—we're worth that much?"
Harry was speechless for a second. Aunt Petunia's focus was… certainly unique. He patiently clarified:
"You are not worth ten million pounds. It's only because you're my family that your souls are priced that high.
"So—want to trade in souls?"
His question yanked Petunia out of her ten-million-pound fantasy. She shook her head frantically.
"N-no, no, we'll use pounds. Pounds are fine."
Even nowadays, the pound had strong buying power. Just using mid-level spells would seriously strain the Dursleys' already modest finances—but that was still better than paying with their souls.
After that, they cleared out the spare room next to Dudley's and gave it to Harry. Once he'd tweaked the contract sigils a bit, Harry signed a contract with the Dursleys.
The entire contract consisted of a single sentence: "The right to interpret this contract rests solely with Harry Potter."
The Dursleys were very unhappy about that, but Harry shut down their protests by force, and they ended up signing meekly.
As he'd put it: "If you don't sign, that's your loss. You don't want to be Muggles for the rest of your lives, do you?"
"Muggle" was a word Harry had picked up from Aunt Petunia.
It was obviously a derogatory term for ordinary people, which did not leave him with a good impression of this world's wizarding society.
The Sorcerer Supreme never looked down on mortals—and as her closest disciple, Harry certainly wasn't going to either.
Once the contract was signed, the Dursleys spent fifty thousand pounds to buy the usage rights to five low-level spells: one for Petunia, one for Vernon, and three for Dudley.
You really had to admit—Petunia and Vernon spoiled Dudley rotten.
It wasn't good for him at all; a kid raised like that would grow crooked.
So whenever he had free time, Harry made sure to "educate" Dudley with a good beating, while Petunia and Vernon watched from the side, furious but too scared to say a word.
By now, Harry had completely replaced Uncle Vernon as the true master of the Dursley household.
It didn't take long for the neighbours—and Harry's classmates—to notice the change.
The boy who used to be bullied all the time had suddenly turned his life around. The Dursleys, who once beat and scolded Harry at the slightest pretext, now treated him with the fawning respect of employees trying to flatter their boss.
Of course, what no outsider knew was that Harry really had become their "boss"—bound to them by a soul-backed contract on the mystical side of things.
Time flew by. With fifty thousand pounds of pocket money, Harry bought himself new clothes and threw away all his old things.
In his newly redecorated room, he spent day and night studying sigils, trying to modify spell structures to master new magic.
With his now-stable chaos magic, he successfully reworked several sigils, boosting his strength yet again.
Time continued to slip by. Just as Harry was starting to think that life in this world wasn't bad either, he finally received the letter Aunt Petunia had mentioned—from Hogwarts.
"Harry, Harry, you've got a letter!" Dudley came trotting over, all deference now, and handed the envelope to Harry with a fawning expression.
After being pummelled back and forth by Harry during this time, Dudley had finally gotten a taste of Harry's former misery and deeply regretted what he'd done.
Even though Harry still bullied him regularly, Dudley now revered his cousin.
Harry's gift of magic was just that useful. Even a simple telekinesis spell made everyday life so much more convenient.
Granted, Dudley's telekinesis was only a low-level spell and could only move about ten kilos at a time.
Harry took the letter from him and glanced down at the address.
Surrey, Little Whinging.
4 Privet Drive, smallest bedroom, second floor.
Mr Harry Potter.