Beta'd by JanieaWolf on AO3
The next day, Harry gets up, showers and feeds Teddy. Once both of them are up and ready to go, Harry sets Teddy with his toys and heads into the greenhouse using the book with the basis scientiam potion in it as a reference for which ingredients he needed. Thankfully, this potion only used plants, and very few of them at that. The hardest part of the potion was how long it had to sit.
Harry figured he might as well do it now, even if he wouldn't need it if the villains didn't want to go with his plan. He could use it in helping others. People would also be more willing to listen to someone with degrees, than someone who just appeared out of nowhere with no paperwork of knowledge.
He gets the four different plants needed for the brew and goes up and back out of the trunk. He sets up in the kitchen with a transfigured pot. He would make it in the pot before transferring it to a few vials that he would need to take in between bouts of chanting. The potion would have to sit for a full 24 hours without interference before using it.
While he works on the potion he thinks about what he could do for the rehab. He'll have a week to start fixing up whichever place he chooses and to make the burn salve for Dabi.
~Time Skip to next day ~
The babysitter, Ueno-San, arrives a few minutes early and happily starts playing with Teddy after Harry explains where everything is. Harry grabs his bag and goes down the hallway to the room he had prepared for the ritual. He had spent a few hours the night before memorizing the repeating chant that went with the ritual.
He would have to repeat "Λαίδη Χέκατ, ακούστε την κλήση μου. Αντιγράψτε τις γνώσεις από τα σενάρια πριν από μένα, και να το θέσει στο μυαλό μου." (Lady Hecate, hear my call. Copy the knowledge from the scripts before me, and lay it in my mind.) 5 times before taking the potion and falling into a deep sleep that would last for no less than 4 hours. In that time, Harry's brain would be working overtime to keep up with the info dump happening.
He sets up the candles in the circle around him, lighting them with a match he transfigured. As he lays down the books he bought for the ritual, Harry starts to gather his magic into his entire body. He lays down in the circle made by the candles, with the books surrounding his head. He starts to chant and feels the air becoming heavy and oppressive with his magic surrounding his body. He starts to black out but focuses on finishing the chant. As the light faded out of his vision, he could feel knowledge start to enter his brain.
~ Time Skip 4 ½ hours later ~
Harry starts to come to, a splitting migraine and bone-deep tiredness overwhelming him. He slowly manages to sit up and move to the prepared bed. He waves a hand and all of the still lit candles are snuffed out with a quick blast of wind. He lays down and retreats into his mindscape.
He has it set up in a mixture of Hogwarts, the Burrow, and the cupboard of his childhood. The Burrow is filled with memories with his true family. All the friends he had made through his years in Hogwarts. Even if they had drifted apart after the horrors of the war, the time they had spent together would always be treasured by him. Hogwarts was home to a majority of his memories. He organized them into the classrooms and Great Hall where the memories happened.
The Room of Requirement was special in that Harry had set it up to be the access point to his magical core. If something happened to severely damage his magic or body, Harry could retreat through this door and recover much faster out of it. Only downside is he is essentially in a coma the entire time he is in his magical core. The memories of the war battles were stored in the Chamber of Secrets.
Finally, the cupboard was all of his bad memories that he would rather forget. All of the beatings from Vernon, all of the "Harry Hunting" by Dudley and his gang. Most of his Pre-Hogwarts time was there. That's also where the deaths of his family and friends were buried.
He slowly sorted the new knowledge into a new classroom he fashioned off the muggle classrooms he had been in during Primary school. He made a set of bookcases that he started organizing by subject. The room seemed pretty empty even after he was done, but Harry figured he would fill it up over the next few months with knowledge of this new world.