While pondering about the history of house-elves was great, it was far from the reason why Harry came to Grimmauld Place 12.
He needed, let's say, a quick fix for his little problem. Something that even he loathed to do but it was necessary.
Basically, his magic was too strong.
His core was bound by Dumbledore and allowed him at most five percent of his vast magical reserves. The same reserves that started rising quite a lot after he started to use wandless magic on a regular basis while being in his most affluent magic growth state since reaching eleven years old. This made these puny five percent of his magic a lot more than what it was previously or what it should have been if he was a normal child.
By all means, he should be only mediocre, maybe even less than that. His severe core-binding should have seen to that and yet. Yet, his wandless magic actually strengthens his own magical capacity. It may not be by much but every spell enhances it by a little. After casting hundreds of them...
Harry didn't dwell on that though. He took it in stride. After all, if it is not broken, don't fix it. He was at best proud of himself that he did something damn right if his magic is getting better.
The problem therefore was...
What would happen if he came to Hogwarts, wand blazing, magic shining, robes billowing, and hair swaying? More importantly, if he was much more capable than he should be?
He would make Twinkles suspicious, that's what. And that simply would not do.
Harry needed to limit his core even more than it already was...
And what a sad thought that was! There was just no other way to stay hidden from Dumbledore's meddling! But he was not looking for something that would bind his core even tighter. That would be shortsighted and idiotic.
Harry understood that even more after reading about several core-binding rituals. What Dumbledore did to his core, can be undone only by Dumbledore or his own magic.
There is also a chance of a special ritual but for that, he would need to know what spell or ritual Dumbledore actually used to bind him. He obviously did not have kiddies safety bind since for anyone else having so much magic blocked would make them into either squib or very, very dead.
When it came to that, Harry was glad. Glad for being Harry Potter. Glad for not keeling over the second he transmigrated.
No, Harry definitely didn't need a complete bind that is hard to revert. He was looking for a limiter that could open and close his access to magic, either limiting or letting him use every bit available to him on his own free will.
Harry was not sure if the Black library had something like that, nevertheless, he preserved and with Kreacher's help, he found what he needed.
Ah, Kreacher, the ever-spooky helper.
Someone who was living in the house, cleaning the library for decades already. The house-elf was an immeasurable resource for Harry. He actually knew well which part of the library to look for the books Harry desired. He just did not know which book held it.
After hours of pondering and comparing dark and darker rituals, Harry chose a simple one.
Core block-key ritual.
A dark ritual first used on prisoners of House Black that was later on adjusted for the children of Blacks themselves.'
Contrary to the brutal dark ritual the Blacks mostly used on their 'toys', aka prisoners, in medieval ages, the one restructured for children is more lenient and safe. It is, however, still dark magic, and therefore something unusable by non-Black.
At least that is, according to the book, how Blacks presented the ritual to the Wizengamot to get it legalized. Nobody cared, to be honest. The government just accepted it without even making an inquiry.
Blacks couldn't be bothered to alter an already existing ritual that obviously worked and they wonder what made 'Black insanity' such a famous concept.
Harry was kinda bewildered.
They used the same on prisoners and their children, with the sole difference being, the black family magics protected the Blacks from the corrupting and mind decaying properties of dark magic upon going through said ritual and even undid the ritual upon their magical maturity unless the 'key' is released sooner. The prisoners though were not so lucky to enjoy such privileges and while it did limit their magic output, the dark magic affected them even more so because of that. It made them constantly feel as if they were put through a mental blender.
Harry's sole solace was he had black family magic and the ritual didn't leave the residue of dark magic. That was, in fact, the most important tidbit. It's un-traceability.
The ritual places a 'block' on the magic core of a child and sets a 'key', a person with the ability to manipulate said block. The 'key' decides how much magic the 'block' lets out, therefore limiting the output of the child.
This serves two purposes.
First, the child's accidental magic won't be too dangerous.
Second, it puts more pressure on the child as he does magic, putting pressure on his core.
Blacks were actually aware that doing so would expand the core, giving them more magic for use. At least, the ancient Blacks were. With how deep the book was buried, Harry doubted anyone younger than five hundred years would have even an inkling of that fact.
Nevertheless, the ritual will help him stay inconspicuous and as average as they come. The less attention he pulls towards himself, the more Dumbledore looks everywhere but him, and the more leeway will he have to maneuver in the shadows.
Harry wasn't having any hopes to match Dumbledore or Voldemort anytime soon if he took the standard path. He did not have time for that. His pitiful few years of magic study would be really inadequate to face against someone studying it for over half a century in Voldemort's case or even longer in Dumbledore's.
After spending his days in the Black library, Harry knew one thing well. He had to stop being childish and reckless.
Even more, caution should be enforced with impunity. As he read through the shelves of dark magic most suited for torture, he almost puked from the visual depiction and the methods there. Blacks were indeed... creative. If nothing else.
As a 'Black' he will too have to get... creative.