Enchanting Melodies (HP SI)

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23 May 1995, Hogwarts, Scotland

Harry was sitting at a desk in the Room of Requirements, with hundreds of pieces of parchment floating around him, each with complicated formulas and calculations. Despite the fact that his new perception of magic made him feel just how fake everything was, the room was still very useful as an impromptu workshop.

Calling it the Room of Requirements was technically correct in the way that the room was extremely good at reading one's intentions and adapting to them, but it would have still been far more appropriate to call it the Room of Illusions because everything was just a mixture of conjurations and fancy illusions, which Harry could easily see through.

They didn't have enough substance, for the lack of a better word, to be real, like a world of falsehoods. To be completely honest, most mages would feel weird staying in this place for too long. It would be akin to staying in virtual reality, it just wasn't real, and for someone like Harry, it was doubly obvious. Of course, the Room of Hidden Things was different, as it was just an expanded space where things were stored or thrown away.

Nevertheless, this was far more preferable than trying to hole himself in an empty classroom. Preparation time aside, the professors seemed to have been granted a way to track down students, probably copies of the Marauder's Map or something. If he had to guess, McGonagall had found the map – Harry wasn't sure who had it before – and made her own copies to make sure that her charges wouldn't be in danger. Either way, Slughorn seemed to have one and kept trying to track down Harry and invite him for tea. Thankfully, they couldn't really find him in the Room of Requirements, and that was more than enough to give Harry enough space to finish his project.

Daphne sometimes joined him, but the young wizard knew that magical experimentation really wasn't something she was passionate about. Currently, she has gone to spend time with Tracy, preparing for the Hogsmeade weekend, which is in a couple of days. Apparently, her entire family was coming, and she wanted to introduce them to Blaise.

There was also the fact that Neville and Hermione kept staring at him whenever he was in public. It was pretty unsettling, all things considered, but to be fair, Harry had been somewhat harsh with them. It wasn't entirely his fault; trying to blackmail him and threatening Daphne to teach Hermione soul magic was beyond stupid because Harry definitely had the upper hand in this conversation and could have very easily gotten out of it. If he had to guess, he'd say that Hermione had probably some form of recording or backup plan in case she ended up getting hurt, which was why he ended up negating everything with his final command to her soul.

There was also the fact that now that he knew more about the field, soul magic was a deeply personal experience. One couldn't be taught soul magic. At best, they could be taught how to perceive souls in some way, but that would be it. The rest were things that depended on that perception. Everyone saw the world in a unique way and souls were no different. What people could do with souls depended entirely on them, and honestly, Harry didn't think Hermione would ever get it.

She was more like a magical machine than a philosopher, and souls were deeply philosophical in nature. It was why soul magic wasn't really a structured piece of magic, not something that could be really replicated. Two people casting the exact same soul magic-based spell with the exact same power could end up with vastly different results, depending on their perception of others and also themselves.

Hermione just didn't have that much insight. If something didn't have a concrete arithmetic formula, she wouldn't have been able to cast it. And so, the muggleborn had been trying to blackmail him by threatening his girlfriend, while also asking him to teach him something that she couldn't even learn. That's without even the connotations of teaching an unstable and frankly arrogant girl a very dangerous piece of magic.

Harry probably should have just explained to her, but he wasn't in a good mood after his conversation with Nimue. Her last words still unsettled him to this day, and so, he lashed out. He gave the muggleborn exactly what she wanted but took away her choice in the matter. He didn't tell her about what she'd lose because he wanted to see her face as she realized that she had lost what had made her special, that she was back to being a normal muggleborn once more.

He gave her soul an unbreakable command to make sure that she wouldn't try to be clever and attempt to blackmail him once more. This was it. He was done with both her and Neville for the foreseeable future; after all, he had a lot more to worry about, mainly, how to actually weaponize the Light and Dark essences to attack their corresponding opposing powers.

It took him a few days of research to realize that both essences were extremely similar and behaved almost exactly the same way, probably because they were designed to assimilate and conquer any dimension they could access. Funnily enough, the essences acted like infections, slowly multiplying using energy, saturating the environment with its presence until it surpassed the original dimension in terms of energy, before very quickly assimilating it violently.

The process was very slow at first, as the essences absorbed energy meant for the other dimension, slowly taking in resources until it became the dominant power. Then it would become very fast. The first stage could probably take centuries just to take over a single dimension, but the second would only need seconds. However, there might be some energy wasted depending on how violently they took over. Then, the Light's or the Dark's will would be more than enough to govern the dimensions – if they were inhabited, of course – or just assimilate it to itself.

Calling the essence a disease wasn't exactly correct. It was more akin to a cancer, slowly growing until it reached a critical mass, and things would very quickly go to shit.

However, something like that wouldn't really work on the Light or the Dark. It would probably take hundreds of thousands of years to achieve something like this and that was without any form of resistance from the Light or the Dark, and even then, all it would do is make the Light and Dark fight amongst themselves more directly, which wasn't exactly what Harry wanted or needed.

No, what he had was the element of surprise. He needed to be quick. He definitely didn't have thousands of years for some slow-acting plan. Ragnarök was coming, and he needed to be ready, and that answer came when he explored the interactions between the Light and the Dark essences. Harry wouldn't be lying when saying that the Light's and the Dark's hatred of one another was built into their very essence. The reaction was… explosive.

It was probably the result of conflicts between the two. They grew sensitive to their enemy's presence. That had a lot of potential.

But what did they sense exactly?

Harry was doing his best to properly analyse the essences, specifically, what they reacted to. They were so similar that just reacting to the energy itself would just get the essence to attack itself. Solomon's magic was the only reason he'd been able to make heads or tails of it.

The magic was breathtakingly efficient. It barely wasted any energy and was made up of more layers and enchantments than the entirety of Hogwarts, while barely using less than a drop of energy. This was, without a doubt, the work of a genius.

As similar as the two essences were, there were other differences. Each opposing and defensive enchantment had very small alterations. They were learning from one another with every confrontation, making their essence, their greatest weapon, more powerful with every bout.

The deeper he went; the more different things became. He had been at it for a few days now, just trying to understand one layer after another, for both essences, trying to understand what exactly had been targeted.

It was extremely draining, even if it was very interesting. He'd have had a lot more fun if he wasn't on a time crunch.

He kept doing it again and again until he found it.

Right at the bottom, in the core of the marvel of magic, was a source. It was, for the lack of a better world, the will of the essence, the thing that contained its central purpose that the Light or the Dark gave it.

The signature was now very clear, now that Harry isolated it, and now all he needed to see which layers detected the opposing signature. Surprisingly, around a quarter of the layers reacted to specific parts of the signature. Damn, the Light and Dark really prioritized fighting one another's attacks.

With the behaviour of the layers of each essence tagged, all Harry had to do was find a way to alter a part of the energy's core enough to trigger a detection signal of a hostile nature. Now that had been very tricky until he realized that changing a very small structure of the core, made it feel alien enough to trigger an immune response from the essence itself. The core of each essence was incredibly resilient, but it relied on a strict hierarchy of layered defences, each one conditioned to differentiate between self and other. By subtly altering a key structural marker—a fundamental component of the essence's signature—Harry could make the Light or Dark perceive a part of itself as foreign.

The trick was precision. If he changed too much, the essence would recognize the modification as internal decay and purge it through natural stabilization mechanisms. Too little, and it wouldn't trigger any response at all. But by targeting the exact signature markers that the opposing essence usually attacked—essentially mimicking an enemy's signature while keeping the rest of the structure intact—he could make the Light or Dark misidentify its own essence as intruders.

He kept altering the essence until he found a perfect combination with a minute amount of energy, if his calculations were correct of course. However, it necessitated an opposing element to act as a template at first, before propagating.

Deciding to take the plunge, he traced a piece of Light essence with the tip of his wand, letting it sink into the depths of the essence's heart. And then, like ripples spreading across a still pond, the reaction began.

The first tendrils of unravelling magic recoiled, sensing an invader where none should be. The Light's defences, honed over millennia to annihilate the Dark, turned inward. Like an ouroboros swallowing its own tail, it began to devour itself. Protective wards flared, barriers slammed into one another, and the once-perfect harmony of magic became discord—like a symphony playing against itself, each note clashing into chaos before the release of energy wiped both of them out.

It worked.

Holy shit, it actually worked.

No, it was more than that. The energy released by a cell attacking itself was more than enough to be harnessed, to infect other cells. Theoretically, only a simple alchemical array to affect the structure of the core of each essence, to be carried from the start, could turn the surrounding cells into infected ones. The change wouldn't even be that big, just a minor shift, which is why it was so efficient.

The initial impact with the Philosopher's Stone and Jörmungandr's Fang for the Dark and Light respectively, would corrupt approximately a realm worth of energy each with just the magic stored inside each one. The essence itself would signal that there had been some sort of attack, and that would start everything. Each entity would target the infected cells, creating more as they destroy it, releasing more energy, and amplifying the reaction exponentially. In mere minutes, the Light and Dark would have destroyed themselves.

It was elegant.

It was beautiful.

It was also not going to work. If Grindelwald truly knew about this, then he could technically get the Light and Dark to change their method of detection and only target the offending object, then work on reversing the damage, and not purge it. It was technically, the only way to stop this sort of attack.

Unluckily for them, Harry had other ideas, which he sadly didn't have time to explore that day since he promised Daphne that he'd join her for an impromptu date on Hogsmeade. They hadn't gone there for a while and everything would probably be crowded during the weekend, since almost every magical family was going to visit their children, having been unable to contact them for months.

Still, he had made a lot of progress so far. The first part of the plan was ready and he could use a break before he did the rest given that it would be very tricky to pull off. He technically had a weapon ready, but there was also the problem of actually deploying something like this. Dimensional barriers were relatively hard to penetrate normally, but something like the Light and Dark, who had fought one another for thousands of years, probably would be a lot harder to pull off.

Jormungandr's fang could pull it off, but it would require a lot of energy, specifically, energy that he was planning on using for the weapon itself. He'd need to find a way to deal with that, either by breaking a prophecy - which was a hassle in itself - or finding some other way to generate the magical energy required.

It always came down to energy, didn't it?

Still, the last few days were surprisingly fun. Harry had forgotten how much he enjoyed researching and solving problems. Of course, he'd prefer it if he didn't have to fight dimensional entities and deal with the possible end of the world, but it was still miles better. Still, he could use a nice break and hanging out with Daphne always relaxed him.

As he left the Room of Requirements, his gut told him that there was something there. Using his Arcane Hearing allowed him to immediately realize that there were people waiting outside under some form of invisibility spell. Were they hoping to attack him or something?

Rolling his eyes, he waved his wand dispelling the illusion, revealing two dark-skinned girls and a boy with very curly hair, their eyes completely wide in surprise. They looked strangely familiar.

One of the girls reacted the first, and released a flash of light, hoping to blind him, only for him to negate it with barely any effort. One of the other girls, who looked distinctively older, sent a weak lightning bolt at him, which he absorbed with the Elder Wand, before dispelling a hard-light Eagle from trying to come at him.

It was familiar, very familiar at that.

This was Blaise's family magic. He spared against the boy while he used it for centuries and he quickly recognized it, enough that he even managed to make a bastardized version of it. He never really mastered it since he found space and time manipulation to be more interesting, but he could still very easily recognize it.

How did the girl have it? Harry knew for a fact that Blaise was the only one left with this magic. It was why there was some pressure for him to return to Italy in the first place. Did they somehow steal it, or copy the crest? No, that was unlikely.

Harry noticed that the boy was conjuring some runes into thin air and decided that he'd had enough questions. Without even motioning everything, he pinned all three of them to the wall, and spoke up, "Now, with that out of the way, why don't you tell me what you're doing here, and also how this girl right there is using the Zabini family magic? You're not supposed to be here, are you?"

Given the panicked looks on their faces, Harry was right that they were up to something very fishy.

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AN: Alright, I'm trying something different in the next few chapters. I was hesitant about putting it but decided to just go through with it. I know that this chapter was a bit of a filler, with a lot of technical stuff about magic, but I haven't really written a chapter with Harry acting like a researcher in a while and it sort of ended up getting away from me. As usual, please let me know what you think and if you have any suggestions.

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If you want to support me check out my patréon at https://www.patréon.com/athassprkr

I tend to upload drafts of early chapters on there to get people's opinions of them so you can read up to 20 chapters ahead as a bonus.

Thank you guys for your support in these hard times.