Strengthening a magical core was similar to working a muscle. It required time, dedication, and effort. The quickest way to do it was to drain every bit of magic out, as safely as possible, then let it refill. The only problem being that there was a fine line between safely draining a magical core and destroying it. Pushing too hard would actually cause it to shatter and kill the wizard or witch in the process.
Along the same principle, but with more control, there was something akin to strength training. The environment also played a part. Using magic in an area full of ambient energy, like Hogwarts or Diagon Alley, was like using lower weight, while doing the same exercises in an area with little to no ambient, Privet Drive for example, was the equivalent of using much heavier weights. The lack of ambient magic meant the magical core had to replenish itself.
The fastest way to drain his magical core would be a quick workout of high-powered spells early in the day. Then, while his core recovered, Harry could turn his focus to his physical training. Keeping his body healthy helped things along as well.
Unfortunately, that wasn't an option. Not only would this draw a lot of attention, from the muggles in the neighborhood and the DMLE. They might not be able to track wandless magic, but the amount of energy he would need to dispel was significant.
Instead, Harry focused on small, precise wandless magic. Using a cutting spell to peel an apple and then summoning the seeds from the core, writing letters by directing the quill with his magic, and transfiguring random items around the house.
Petunia had found an old box of tin soldiers that they had bought for Dudley years ago. With a bit of concentration, Harry was able to animate the figures. It quickly became a game that took over the wide coffee table in the living room. There three colors, one for Petunia, Dudley, and Vernon. They would instruct Harry how they wanted their troops to do, and then he would move them. The soldiers were limited to blades and arrows, their muskets and cannons worked a little too well. Vernon's chair had a spattering of burn marks now. They had also added a couple of old mugs, a bundled-up sock (much to Dobby's horror), and a stack of coasters to vary up the landscape.
Even with all that, it still wasn't pushing his magic as far as he needed. On a whim, Harry tried to change his hair color. Much to his surprise, it had worked. He wasn't a metamorphmagus like Tonks. She could change effortlessly with a thought. Any changes he made took considerable focus and magical power. This discovery led to a new evening ritual. Harry would spend about an hour in front of the mirror cutting his hair, changing the color, then growing it back out and returning the natural shade. Once exhausted, he would shamble to his bed and pass out.
He didn't trust his skill enough to mess with anything more. Changing his bone structure, even the cartilage, was no easy feat. The skin was even more complicated. He did have success with his fingernails and toenails. Harry could trim, grow, harden, and sharpen them. Having claws at will was something he was going to keep a tight lid on.
Harry could already feel a noticeable change by the end of the second week. Just in time for the twins to visit. Much to Arthur's joy, they took muggle transit to the house. Harry stood out on the front lawn watching as a cab pulled up in front. Arthur stepped out, a bit ruffled but still grinning like a loon, followed by a just as messy Fred and George.
The twins opened the boot of the cab to get their bags. They were only staying for the a few days, but they came prepared. Harry watched them struggle to get their bags out for a moment before coming over to help. The twins were skilled in a great many things, packing things without an expansion charm was not one of them.
"And how much was that?" Arthur leaned back speak to the cabby.
Harry didn't hear the amount, but he did see Arthur hand the cabby a wad of cash. Considering the exchange rate from galleons to pounds, even a couple hundred was pocket change. The cabby quickly hopped out of the car and scrambled to help them unpack.
Arthur turned around to admire the Muggle neighborhood. He gave a wave to Mrs. Figg, which would have been suspicious, except Arthur then waved at every person he saw. The man was having a blast.
"He's been grinning like a loon since we got off the train." George chuckled. "It was the same as one of ours." Fred shook his head. "Better graffiti though." George turned to his twin. "Leagues ahead of the Express." Fred nodded. "Might need to get a telephone machine to call all those numbers." George smiled.
Harry didn't even try to fight the smile that crossed his face. His attention shifted to Arthur as the man began to approach the house. The mans' broad smile began to faulter as he got closer. His foot came down just a bit too fast, causing him to stumble for a step. He stared at his sons, then Harry, and finally down at his hand. His left hand. Arthur's face scrunched up in grief Harry had only seen once before.
"He crossed the wards." Harry muttered.
He slipped between the twins, carefully approaching the man.
"Arthur." Harry spoke softly. "Come inside, so we can talk."
"Harry?" The mans' eyes snapped up to him. They were red, filled with tears.
"It's a lot." Harry continued to move closer, holding his hand out with the palm up. "It was for me too. Come inside, we can talk. It's safe."
Arthur straightened up, there was a strength there that hadn't been before. He nodded. The man grabbed the bags and strode purposefully toward the house.
"What happened?" Fred asked, his voice void of the usual cheer it had.
"Do you two feel any different?" Harry asked.
Fred looked to George, who shook his head. The twins looked back to Harry and shrugged.
"That's a relief." Harry whispered. "Let's talk inside."
Vernon opened the door as Arthur got closer.
"Arthur, I believe?" His uncle held a hand-out. "Haven't been properly introduced, Vernon Dursley."
Arthur shot a questioning look to Harry. The young man nodded. Arthur shook the offered hand. Vernon took in the sight of the man.
"You too, eh?" Vernon sighed. "We'll fix you a cup of tea."
Harry headed inside with the twins a step behind him. Vernon had already led Arthur into the kitchen. Harry closed the front door behind them, then locked it with magic as well as the deadbolt. The twins shared a silent conversation before moving deeper into the house. The trio made it into the kitchen just as Arthur and Vernon were sitting down. Petunia humming to herself, reading a newspaper.
"Pet." Vernon spoke softly. "Could you make a pot of tea?"
Dobby popped into the room. "Dobby is on tea duty today."
Vernon laughed. "Dobby, my good elf, would you make us a pot of tea?"
"Take a seat." Harry offered the stunned twins.
An uneasy silence settled on the room, only broken by the sound of Dobby griping at the electric kettle.
"Last year." Harry started. "I was bitten by a basilisk while rescuing Ginny. The venom killed me for a moment. Instead of dying, it destroyed a horcrux that had latched onto me. Once it was gone, I started to see things, and remember things, that had been kept from me. When I got home, back here, I put wards in place to protect myself and my family. Protection against compulsions, memory charms, and other mental magics." Harry motioned to his aunt and uncle. "You can see how much that has changed things."
"What does that have to do with dad?" George asked.
"Think you know already, George." Fred whispered.
"The potions, compulsions, and memory charms have been removed." Harry gazed at Arthur.
Arthur made to speak but had to clear his throat a few times before the words could come out.
"Boys." The man looked to his sons. "I love you, and your siblings with all my heart. I truly do."
"But not, mom." George whispered.
Arthur shook his head. "How?"
"Not sure." Fred shrugged. "Could be the twin thing." George added. "Can't be compelled." Fred continued. "Mind games just don't work on us." George nodded. "We've tried to tell you before." Fred's voice dropped to a whisper. "You always forget." George matched the tone. "Always." They said in unison.
"Molly?" Harry asked.
The teacup in front of Arthur shattered. A bubble appeared around the explosion, putting the pieces back together.
"Thank you, Dobby." Harry said.
"One sugar for Vernons, cream for Tuna, and coffee for Harry Potter sir." Dobby moved around the table with eases. "Frog and Gourd want tea? Mister Wheezes?"
"No thank you." Arthur managed after a deep breath. "Yes. Molly." The name dripped with venom. "Years upon years. Compulsions, potions, and memory charms." He looked to the twins. "How long would it take me to forget?"
"An hour at most." Fred waved off the cup of tea. "Most of the time quicker." George nodded, holding up two fingers for sugar.
"Anything from Dumbledore?" Harry looked over to Arthur.
The man shook his head. "How long will this… clarity last?"
"If you trust me." Harry said. "I can make sure it stays."
"How?" Arthur met his eyes. "My trust is fragile right now."
"Three ways." Harry said. "The easiest, and messiest, would be a divorce. One test from the goblins and it's done. The second, more complicated, would be to create a magical contract that binds Molly for harming others. You would have to get her to sign it though."
"Nothing that can be done before leaving the protection of the wards." Arthur sighed. "Divorce would destroy our family."
"You said three." Vernon spoke for the first time.
"It requires Arthur to trust me completely." Harry kept his gaze on Arthur. "Swear fealty, as the head of House Weasley, to House Potter. You would be under my protection, regardless of where you are."
"That doesn't sound too drastic." Vernon shrugged.
"It would mean that I would control House Weasley." Harry shifted to look at Vernon. "Any attack, from within or otherwise, would be seen as an attack on House Potter and the magic would react in kind."
"It would kill her." Arthur whispered.
"Almost certainly." Harry nodded.
"Well." Fred grabbed the flask from his father's jacket pocket, poured a good shot into George's teacup, and downed it. "That's some shit." George finished.
"What about the wards you drew around the house?" Petunia asked.
"They wouldn't work long-term." Harry answered. "Two to four weeks, depending."
"And they need blood." Arthur took the flask back and added some to his tea.
"No." Harry shook his head. "They can be done without blood. Ink works just as well. They would just need to be in a place she wouldn't see."
Arthur chuckled. "Anywhere from the neck down then."
"You two don't…" Harry let the words hang.
"Harry." George scoffed. "There are certain things a child doesn't need to know about their parents." Fred shuddered.
Arthur smiled at his sons. "No. Maybe for an anniversary or birthday."
"Alright." Harry rubbed a hand across his face. "I'll draw some runes on you. Don't count on them lasting more than two weeks. Is that enough time?"
Arthur let out a long, tired sigh. "It will have to be."
"Whatever you decide, dad." George smiled at his father. "We are with you." Fred finished. "Ginny too." George added quickly. "Maybe Ron." Fred continued. "Not sure about Percy." George shook his head. "Not sure what went wrong with that one." Fred shook his head as well, their movements syncing up.
"Follow me, Arthur." Harry stood. "We can get this finished and move on to happier things. You're in a Muggle house, surrounded by Muggle things, with actual Muggles to talk to."
Arthur smiled. "That is true."