Dreizehnn
Oh! Glad that I managed to capture your interest. Okay. Here how I imagined it would work. Let me point this out: 1) One of the main things in Nasuverse is a concept of Mystery. What I understand from it. It can be history and stories imprinted upon an object, action or natural effect. Or it could an act that is possible to naturally exist, but performed unnaturally. 2) Divine Core is a god’s metaphysical soul. You could say it their soul as a god. There could be Greek Zeus and Roman Jupiter. Different personalities but their origin is the same. (For example. Angra Mainyu is a strange God. He was born Human, but through others’ wishes and horrifying rituals he became a concept of All the World Evils. He is not a God, yet he is. Because of accumulated energy in Grail (no wishes were granted) and Einzebern’s fuck up, he possessed the Grail. He normally would not be able to get a wish that way. But the wishes of his village’s people of him being the Angra Mainyu are a significant part of him. So any wish Grail would grant from now own will result in the birth of Angra Mainyu. So, Grail in this situation became his Divine Core that is connected to to him, but not completely. What my idea is to repeat the Mystery by which the All the World Evils was created. But only the polar opposite of it. Shura Mazda, Zoroastrian counterpart of Angra Mainyu. But Roman does not need all that ritualistic crap. He can use his Abilty that allows his Magecraft to get the closest to the True Magic. Get some artifacts or symbols of Ahura Mazda (or maybe yet, get something with Angra Mainyu Mystery in it and inverse it), use Excalibur as the source of All the World Goodness (Dreams and Hopes). And wish for the birth of these two Gods. They will begin to attempt to fuse with the only empty Divine Core available , the Grail. And by their nature and origin, cancel each other. Leaving an empty Divine Core. Roman will become a Nameless God. With no Authorities. A Mortal God that does not have to move to the Reverse Side.
That’s the thing. Neither deity of Zoroastrism exists in Nasuverse more than a concept. Angra Mainyu as a God only started to exist when Avenger possessed the Grail. Meaning that Ahura Mazda exists as a concept. My understanding of this is that True God Angra Mainyu and all other Zoroastrian Mythology did not had time to be born through human belief. Avenger became god when he was human. But because the only thing left of him when he died was his hatred of humanity, he failed to become God. Looking at how thing work in Nasuverse, I think that the only way for Ahura Mazda to be born was thru the same ritual. Which did not happen. (Someone made an Alternative Shirou Emiya as a potential Ahura Mazda. Like, what kind of person Ahura Mazda could be as a human before his ‘ascention’). As for his Divine Core? Still the Holly Grail. Why? Every wish that anyone will …wish for would result in the birth of Angra Mainyu. Why he cannot use his Divine Core? Because no one has asked for that wish. That’s why I’m Heavens Feel route he needed Sakura to be his body and the one to wish for his Birth. The thing is. By condemning Avenger to become Angra Mainyu something good did happen. People’s nature did improve a bit, they become better….outside of torturing Avenger. So you can make it so that there was some minuscule amount of All the World Good in Avenger. Because he did bring them piece of mind. So Angra Mainyu and Ahura Mazda will exist in the same Divine Core for a bit before cancelling each other.
Dreizehnn:but in this, wouldn't it require for Angra Mainyu's counterpart to not be existing beforehand? In Fate, all Gods do exist in some shape or form. At the same time, if the mystery gathered did actually let said God be summoned there, they would take the nearest compatible body as a vessel for themselves and manifest in the world through it. The fact that homunculi would be needed for this ritual makes it worse because Homunculi are essentially the perfect vessels a God could ask for. Recall Ishtar manifesting in Fate/Strange Fake for reference. Furthermore, going by your theory, the Grail can only function as a Pseudo Divine Core because Angra Mainyu is in it. Were his counterpart to be actually summoned, that God would be a far more powerful one and have more leeway to use his Divine Authority. Instead of cancellation, he'd destroy the Grail completely to get rid of his rival. but ignoring this, even if they did cancel each other out, that would just make them both disappear from that point in time and at the same time, the Grail War would also lose what makes it function as a core. Do you have a way around these problems? Yours is a pretty neat idea and it may even work with some tampering.