The Saoshyant Project - Worldbuilding 

Uhmmmm... well... you see... Angelic technology let's you detect divine beings through the astral plane using second order causality

In the long version of the story there is a section where a couple of the pilots are discussing was Ahura Mazda actually was. One of them argues that he wasn't God, nor a god, because he died, didn't know everything, wasn't all powerful, and so on. Then another pilot argues that whatever Ahura Mazda there's no doubt he created life, and was more powerful than humanity can ever hope to be, thus the term "god" could apply. Finally they ask the angels what Ahura Mazda and Angra Mainyu are, and the angels explain that they are not sure, Ahura Mazda never told them. The only thing they know is that at some point there were many more like them, then there were just two, and now there's only one, of whatever they are

Story Time: When I was in highschool a classmate told me about Evangelion and he described the plot of the entire show to me, but he did so very poorly I imagined the few remaining humans living in a tiny fortress perpetually being attacked by angels, and I thought that was cool as fuck When I finally watched Evangelion it was quite different from what I had imagined, but I still liked it a lot Then one day I was thinking about Zoroastrianism and their belief that Ahura Mazda will defeat Angra Mainyu, but then I thought "what if he doesn't?, what if he looses?, weren't we supposed to help God in this cosmic battle?" That idea merged with my first impression of Evangelion and developed into this

Here's the short version: First we meet the main characters, pilots, government workers, scientists, technicians, stuff like that. We are presented with the world which is pretty much what I said in the video, except there's also a secret cult that worships Angra Mainyu After a few battles with the demons the audience is getting used to the rythm of things, but that's when Angra Mainyu is detected through the Astral Plane, there's one year of time before it arrives During this year a ton of stuff happens and most of the characters die. The most elite pilots who had a chance of beating Ahura Mazda are killed when their forstress is destroyed, most of the technicians and scientists are killed, so there's no hope to develop a secret weapon, what remained of the government collapses The remaining characters are not part of anything now, they are just people who happen to have a few artificial demigods they can pilot They don't even know if there are other humans alive, since all the fortresses were attacked and they lost communication The day before Angra Mainyu arrives the remaining characters dream about it, and they talk to it, and Angra Mainyu explains that humans cannot understand the goals and motivations of beings such as it and Ahura Mazda. We think Ahura Mazda was good because he gave us life, but his purpose wasn't to give us life, and Angra Mainyu doesn't want to kill us, both are just means to goals we cannot understand, but Angra Mainyu insists that if we could understand we would be on his side, and pleads us to trust him, that it will all turn out okay after it destroys all life Finally Angra Mainyu arrives, the pilots fight valiantly against it, but they are basically fighting a shadow, a projection of the being into the physical plane, and every second more of it is projected, making it stronger As the fight goes on all the remaining characters are killed or maimed, and it becomes increasingly clear no one else survived in the other fortresses, they are all that remains The remaining characters decide to give up, and Angra Mainyu starts killing them in a peaceful manner, they don't suffer, but when there's only one left he or she still fights back, but this is not to protect anyone, because no one is left, this is not to survive because they are wounded and will die soon anyway, this is not to defeat Angra Mainyu because it cannot be defeated anymore Angra Mainyu is perplexed by this, and considers that with Ahura Mazda being dead, the creatures he made can no longer serve their original purpose, the one Angra Mainyu disagreed with, but instead it is free to do... something else, it doesn't know what it will be, but it reasons life has earned the right to get to it, whatever it is Then Angra Mainyu lets itself be killed, and humanity is left in a world without Gods, without demons, in an empty world, alone. Was it worth it?

The lore of Fate is completely incomprehensible to me

If you do, I'd make a video about it

As long as you don't make money out of it, sure. BUT if you do want to make money of these ideas, like publishing a book, I'd ask for an 80-20 split, or something like that