Laying foundations
Harry woke up feeling refreshed. The beginning of a new life was, by now, almost routine. He liked to throw in some variety, but on the whole the day almost always ended late. He glanced out his bedroom window and saw that the sun had well and truly risen. It was at least noon.
Going through the morning routine he had perfected was done without much conscious thought. Instead, Harry's mind was focusing on creating a list of things he needed to do before school started. Getting some projects done for the goblins was a necessity, seeing that it would be his only source of income for the foreseeable future. Many things Harry could do without actually buying things, but there were some he needed money for. As his stomach reminded him, food was one.
Magic was strange, and the majority of that strangeness came from the fact magic was anthropocentric. Almost all of it related in some way to humans, and the way humans perceived it affected how magic worked. There was no real reason for the levitation spell's incantation to be Wingardium Leviosa, except that was what magical folks believed the spell required. Separating the intent and will for something to happen from the trappings of how one went to achieve that was a major part of silent and gestureless casting of spells. It had taken Harry seven lifetimes to work that out and perfect his use of such magic.
Ritual magic was even more tightly tied to expectations. These days most ritual magic was deemed Dark, and that expectation colored the rituals themselves, both how they were performed and what they did. Coming up with new rituals that didn't require a sacrifice of some kind and had a beneficial effect was difficult with the restrictions belief placed on them.
Still, Harry had had plenty of time to develop a few of his own. The most important was a ritual to transfer Horcruxes from one container to another, something that was, for obvious reasons, quite essential to him. Due to the nature of Horcruxes the ritual did require a sacrifice, but Harry had managed to minimize the ethical impact. The ritual needed the life of any creature, no matter how small or great.
In remembrance of Ron's fear of spiders they were Harry's preferred victims. So when Harry Apparated from the parking lot of a McDonald's to the alley behind Leaky Cauldron he captured one from the corner before setting out to Diagon Alley Disillusioned. Harry walked through the alley to Gringotts, and was escorted down to his Vault.
After making sure the Vault was secure Harry conjured the tools required for the ritual and took out the receptacle of the Horcrux. Harry preferred these things to be simple, worthless, and recognizable, so in this case the new Horcrux would be a green-painted rock he had collected from the Dursley's driveway.
The ritual itself didn't require much. A conjured silver circle on the floor in which he placed the immobilized spider, bright light which he achieved with flashlights, and a drop of blood from him. The Horcrux would pass from him, through the circle, to the stone on the other side.
"For the life preserved, life taken. For the life taken, soul shattered. For the shard, a container. Now, with another sacrifice, transfer that shard. With this life taken, transfer the shard. Through blood, silver, and life, the shard is transferred."
The pain was excruciating, something Harry had not considered when creating the ritual. Tom Riddle's Horcrux had been intertwined with his own soul for nearly all his life, so it should have been obvious to him that it had well and truly settled, and that removing it would tug at his own soul. Sadly, after establishing the ritual it was nearly impossible to change. So every time Harry used the ritual he was left gasping on the floor, with tears of pain flowing down his face.
There would be a sensation of chafing skin inside his head whenever he'd use magic for the next couple of weeks, but it was well worth it for Harry. Sharing a body with Riddle's Horcrux was offensive to him, and he was glad to get rid of it in a manner that didn't require his death.
It took minutes for Harry to get up from the floor. He Vanished the spider's remains, and tossed the rock to the far corner of the Vault. Later he'd get some equipment and furniture here, for a truly private workshop, but for now the ground was good enough for the blasted Horcrux.
Harry left his Vault and went to the goblins, asking what would be required of him. With a few cunning questions and suggestions he landed the job he wanted. By taking the task of upgrading Vault security he'd have access to many of the Vaults, and would be able to stop Quirrell before he became the Defense Teacher at Hogwarts. Harry had grown quite pragmatic over the years, and saving Quirrell was far too much work for too little gain. The man had, in the end, been a willing accomplice with Tom Riddle.
The first Vault Harry and Krandala worked together on was Dumbledore's where he kept the Philosopher's stone. Like before, he changed the protections in a manner that would capture would-be thieves instead of attempting to kill them outright. The curse would render them incapable of speech and movement in addition to trapping them inside the Vault door, making escape nearly impossible. To add to the effect a strong Stupefy would be applied. The combination wasn't pleasant, but it wasn't deadly either.
The truly ingenious part were the more obvious protections applied to the surface of the door and walls, both inside and outside. There was a good chance that less capable thieves would be stopped by these, while the protective enchantments and curses hidden inside the door would go unnoticed.
If Harry had more time, and interest, he'd probably layer the door even more. Gringotts' Vaults had big doors, so each layer would offer additional space for enchantments and curses. It was likely that he'd do the work on his own Vault, and probably a few others once the goblins got wind of what he was doing. It was worth the extra work.
Eventually the week came to an end, and it was Harry's birthday. He woke up with a predatory smile. True, Hagrid would be picking up the Stone today, but Quirrell would still be trying to get it. Riddle wouldn't want to stay trapped in the door, so he would leave Quirrell's body, effectively killing the poor bastard. Harry knew that the snake would be coming to Hogwarts regardless, in another body, but at least they'd get a better teacher this way.
Harry had worked with Krandala daily, enhancing the security of the most important Vaults first. One of those was the Lestrange Vault where one of Riddle's Horcruxes was. By now Krandala trusted Harry quite a bit, and left him on his own for hours at a time. She didn't exactly announce her returns or leavings, though, so Harry worked fast when he replaced Helga Hufflepuff's Cup with a nearly perfect replica. Even knowing the magics of the Cup he couldn't match the magical signature perfectly. There were very few people alive who had seen the Cup before, though, so the replacement would fool everyone.
Harry celebrated his birthday by placing the hair of a decent-looking non-magical into a flask of Polyjuice Potion. So armed he went looking for Jasmine and Edward Melbourne, a voracious swinger couple. Melbournes rarely declined a tussle, and to them the gender of their guest mattered very little. Harry had become fairly friendly with them over his lifetimes.
To keep up appearances Harry went shopping the next morning. He needed to buy everything from the Hogwarts list, even if he knew the contents by heart. It was always great to see Hedwig, even if the owl was confused for the first week of their renewed acquaintance. Unsurprisingly Harry also got a lot more than needed, and dropped them all into his Vault.
The meeting with Ollivander had been fun for the past twenty lifetimes. The old wandmaker was imbued with the magic of the various materials he worked with, and as a result was far more perceptive than your average wizard. Harry knew for a fact that Ollivander could see much more than Dumbledore, even if he didn't always understand what he sensed.
"Welcome! Welcome to-" Ollivander greeted Harry only to be struck speechless by what he sensed.
"Ollivanders Wand Shop!" Harry quipped. "No, really, Mr. Ollivander, please sit down. We have something to talk about."
"Whatever you say, Mr.-" Ollivander said, finding a seat.
"Mr. Potter. I'd be grateful if you wouldn't spread it around that I'm back. I'd rather not get all that attention, you understand?"
"Oh, certainly, Mr. Potter."
Harry conjured himself a seat and put up a note "Out for Lunch" at the door before locking it.
"Now, I know that it's fruitless to try to convince you that I'm an ordinary eleven-year-old, so I won't try. Instead, I'm going to tell you a hypothetical chain of events that led to me being here in front of you."
"I... see."
"I doubt it, but you just might after this.
"Now, there was once a boy, let's call him Harold, who was revered by the magical population of Great Britain, and some beyond it. He was, if not bright, at least hardworking, and managed to gain many friends. One of these friends was very bright indeed, and after Harold vanquished a terrible foe, with some significant losses, I might add, this very bright friend had a thought. What if Harold got a second chance? Would everything end up better? Now, this very bright friend of Harold's was aware of time manipulating magics, and became an Unspeakable to study it further. While they studied and experimented the world marched on. The non-magical population of the world had, over the decades if not centuries, managed to do irreparable harm to the whole planet. Once the magicals realized that the threat was very real there was no longer anything even magic could do. So the world succumbed to anarchy and war. Harold tried to fight for justice and what was right, but was doomed to fail.
"Harold's very bright friend, however, made a breakthrough that could change all that. After decades of research they managed to create a ritual that could send one person back in time. That very good friend of Harold's had been following Harold's life, and decided that Harold had everything needed in a savior, except for a few things that they could fix. So when the situation got really desperate, the friend decided to act. They thought it was pointless to ask Harold for permission, or, indeed, give Harold any chance of wriggling away from what they were planning to do, so they Stupefied Harold. Now, Harold was quite accomplished in combat magics, but why would he be on his toes with a very good friend?
"So Harold woke up tied to a slab of stone, with his very bright and good friend leaning over him. Harold could hear sounds of combat coming from somewhere, and his good friend was quite disheveled. Rather than explain anything the friend finished the ritual they had devised, and watched as it spirited Harold back in time.
"There was, of course, a twist to the ritual. Instead of being one-time ticket to the past, it had some unknown trigger to end. As long as Harold hasn't triggered that end, he will return to the past once he dies - or is about to die.
"Now, Mr. Ollivander, after hearing this purely hypothetical chain of events, do you think you could stay quiet about what you have sensed, or do I have to alter your memory? The latter is rather onerous, as I would have to do it every time we meet."
Ollivander swallowed, watching the small boy in front of him with eyes wide open, barely daring to breathe. "I'm sure I'm capable of staying silent, Mr. Potter."
Harry smiled. Ollivander always understood. "Great. Now that the pleasantries are over, perhaps I could bother you to let me buy one of your marvelous wands?"
Ollivander relaxed. "Of course, Mr. Potter. Do you have a preference?"
"Well, considering my history, let's try with Voldemort's wand's twin, shall we?"
Ollivander merely glanced at Harry before standing up and fetching the wand. "You know you're taking all the fun out of this, don't you?"
"I do, Mr. Ollivander, I really do. Perhaps I can pay you back by discussing improvements for creating wands? Maybe we could converse about exotic wand materials?"
There was a glint in Ollivander's eyes as he nodded. "That would be most pleasant. Now, the price for that particular wand is seventy galleons."
Harry smiled and handed over the coins. Ollivander's expression fell. "You knew I was going to ask for that, didn't you?"
"I'd be lying if I'd say no, Mr. Ollivander."
After leaving the shop Harry went to get an ice cream and to read the Daily Prophet. The main headline was "Hogwarts teacher found dead in Gringotts!" and the article barely mentioned his attempted theft, instead focusing on how goblins' defensive measures might be "slightly overzealous" despite several quotes from rather important families that were approving of these security improvements.
The ice cream was as delicious this time as it had been the last thirty-two times.