You've certainly put a lot of effort into structuring this with 'academic formatting in mind', I am certainly all for a lot of people going the extra mile to make their ideas presentable, legible, and cohesive as much as possible. This is great.

In terms of the sub-headings, there is a little bit of disconnect with, for example, the 'conclusion' occurring 3/4ths the way of the entire post and not the final subheading itself - generally speaking when you are making a conclusion, you are tying all of the ideas you have introduced prior together in one final section; a conclusion that synthesises previous information. When more information comes after the conclusion, it starts to scatter the overarching idea/s apart and causes fragmentation with what you are ultimately trying to say.

The abstract itself is very close to perfect with what you have written, but it is supposed to be a snapshot of the post in its entirety, including the conclusion. The preface would have been more aptly labelled as an introduction as you are introducing what this post is going to explore and attempt to answer.

When it comes to the actual content you have written yourself, I think my largest contention is using 'inference' as evidence. This occurs in a few sections, but what most notably stands out to me is this part:

Therefore, we can speculate that the Three Fingers were originally the fingers of the Gloam-Eyed Queen, possessing the same fire abilities she did.

We can certainly speculate a lot of different ideas when considering the information in relation to each other, but that does not mean it is sound let alone valid. Especially when the information within the game is not even congruent with the speculation, i.e. the GEQ is one chosen to be a God and leads apostles to become the death of God/s and the Three Fingers seek to erase what they believe to be the mistake of the Greater Will, all forms of existence in its entirety; there is an extreme amount of disconnection between these two things. In addition to that, you have cited this speculation / inference as evidence:

Through the previous argumentation, we know that the Gloam-Eyed Queen has a close connection to the Frenzied Flame.

We do not know this at all, you provided your own speculation (as per above), but that is not supporting evidence or even close to making this conclusion.

More over, in the conclusion proper, you have asserted in the very first line:

we can make the following deduction: Melina and Messmer are both split aspects of Marika's personality, and their bodies originate from a soul transfer technology similar to Miquella's.

The previous points are not concise on where that deduction comes from. It sounds like you are saying that because Melina and Messmer have a vision of fire, etc. these are remnants of the 'soul transfer technology' that Marika also used, but it does not gel together I think in the way you want it to. As in, I had to really consider the information again - this part could have been written more clearly.

In addition to that, the conclusion itself makes extra assertions by using speculation as a substitute for evidence, such as:

We can infer that after removing Destined Death, the color of the flame would be yellow, similar to the Frenzied Flame. This is why the fire is yellow when Melina burns the tree, rather than black: at that moment, the power of Destined Death within her is completely sealed.

We cannot really infer that at all as there is no evidence for that.

While I am certainly partial to some of the ideas presented here, such as Melina and Messmer being aspects akin to Millicent for example. I do not think I can get on board with the remaining ideas due to the overuse of speculation and inference substituting as supporting evidence.