Harry's POV
As the months passed, while the school continued with the card duels, Harry kept his schedule on track.
In his studies of DADA material he finished seventh year, he would have gone beyond it but he couldn't find any book about advance material, no dark arts, no old auror's guides, no spells which needed some sacrifice nor even any mention about souls in any book.
And while he completely understood why there can't be any books about sacrifice nor any book about dark arts, as the ministry forbid it long ago, not having any book about souls? Soul related magic couldn't be all bad, no, it was in the hands of one Albus Dumbledore, the only reason why.
Another thing that improved was his transfigurations, he was now in seventh year's transfigurations both in control and in practice.
The second half of the sixth year material was about transfiguring unimportant body parts of human body, transfiguring his feet to either stone or metal, and then to animal parts like making claws and in the end to plants.
The seventh year is about about transfiguring important body parts, lungs, heart, head etc...
The problem was that changing your body parts was dangerous, as getting metal poisoning by transfiguring your feet and the blood in it to metal was a terrible way to die and while he managed to get around that by using dead bodies he 'borrowed' from closed caskets, it did make him feel guilty.
Yet that brings him to the third thing he improved on.
As he already stole bodies, he decided to use them for good, for science.
Which meant he started once again learning medicine, leaving behind Quantum mechanics and engineering for now, and started doing surgeries on the corpses he acquired while on history and divination he read about it, managing to reach fifth year out of seven on his way to become a full fledge doctor, which helped speed along his transfiguration.
Another thing him getting bodies helped in was rituals.
As per the agreement he had with the Greengrass family, he got every ritual book the family managed to get their hands on, and after scanning the books into Gai and having it read it to him while he went through his physical and magical workouts to keep in shape, Harry got theoretical understanding about rituals.
Rituals, in their essence, are a combination of runes and heavy magic.
As the books explain it, there are two kinds of magic, light and heavy.
Light magic is the regular magic, magical people do each day, it is the charms and transfigurations they teach us in school.
Heavy magic is the one they call dark, a mistake that came from the people who only used light magic- not light as in brightness, but light as in non-heavy.
Heavy magic is magic that take a lot of magic or need something to be sacrificed to succeed. It is potions, dark arts and rituals.
While light magic takes only your magic to work and once you don't have enough it stops, heavy magic takes any payment as possible, magic, ingridiants, emotions, and even parts of your soul.
It can be considered as beginner's and advanced magic.
Beginner's magic is based on taking the material that is in it's original state and use it, like using coal to make fire.
Advanced magic is like processing coal into diamonds. It loses most of it's properties, yet gain unique hardness, but to do so you need pressure, the extra ingridiants, emotions or other stuff are that needed pressure.
Which creates the problem with most of the heavy magic- it needs tons of preparations, and specific ingredients.
In fact, there is only one heavy magic that don't need preparation and it's because it, is a preparation- the killing curse.
A curse of which the true purpose of is to break the caster's soul and the killing is only a side affect of the discharge, which is why only one person is known to use it regularly in fights, the one who doesn't care about his soul fragility, and the tears it cause to cast this curse even without the other preparation needed for a full horcrux, which is why a fake Horcrux was created in either Harry or Marcus.
So, after realizing what rituals are, and having no book about 'the dark arts', Harry decided that for him to study rituals he needed to see the effects they have on the human body, and started to use the bodies who were already transfigure and untransfigured, which were opened and closed with surgery cuts all over them, for basic rituals.
He started by using a ritual that controls the level of melanin in a person's eyes, therefore granting the dead bodies different eye colors, he then moved to hair color and skin color before moving to more advanced stuff.
His biggest problem were the inability to know how it might affect a person's psych, and the lack of resources, as each ritual needed references, so if he wanted green eyes he needed a person's green eyes in a ritual. but it helped him know in knowing one thing, some materials can be exchanged with knowledge. By putting runes that explain the melanin level needed, the need for green eyes was lost, instead he needed more magic, for which he had to be thankful for the card duels that made sure he has more then enough.
His repeat use of rituals made his runes expertise grow.
while he still can't curve them good enough, only doing so in class, otherwise he used Gai to do it for him, he started understanding the relationship between the faith rune has power and the fact it does.
Runes never were, nor ever would be magically connected, it was always about intent and knowledge.
By thinking, no, by knowing runes are magical they become magical to you, just like how by believing saying a spell make it work, make it work.
The knowledge something is true make it so with magic.
Yet that raised the question, was following science in doing magic is the right way? Could it be that all his warm confirming to the rules of science just made his magic smaller, weaker then it could be?
To answer this question Harry broke one of his rules, he created a new personality in his mind, one that doesn't know science.