Worm stories are always welcome, and you are a great author so I'll be sure to look into that later on. Will you use PHO interludes? Thanks for the story, it's been really fun so far.

Looks good, but there's only so much you can really get out of AoT, fun snippet regardless.

My guy, The Sins of Humanity Beasts in Nasuverse are of course going to be ridiculously strong with their own individual and innate abilities. They are absurdly dangerous, second only to the Ultimate Ones, and with few exceptions like The Umbral Star's Vanguard: Velber who destroyed all Earth's landmass in sixth lostbelt, and the Lostbelt King Zeus. But again, your comparing the top figures of a stronger series, of course they would steamroll. The Black Barrel alone is too strong of a weapon to exist in DxD, it'd be like having 'Gun God' from Notes, someone capable of killing Aristoteles. But DxD isn't weak by any metric, this is an Ecchi focused world, and they were still planet busting level by the end. I'm sure the author is gonna buff the characters a little to be a more threatening, just look at DxD Angra Mainyu, he was kinda pathetic in the novel (with a terrible design), but he feels ominous in this story. Anyway...I feel like we got way off topic, this seven headed figure is clearly related to DxD's Trihexia, the Beast of Revelation. I feel like you focused a little to hard on the word Beast, this Fate images were just for visual purposes, because they look amazing, and are Iconic.

The Beast of Revelation is something from the Book of Revelation, the final book of the New Testament, and thus the Final book of the Bible. DxD Is a series with alot of Christianity thrown in since it's an integral part of the canon casts' faction, so it has a lot of Christian tones when world building. Trihexia the Apocalyptic Beast(Name literally means three six's), has alot of Beast of Revelation tones because it had a similar role of causing an apocalypse in the Bible, even sharing the 'Ten horns' and various animal features as the Beast of Revelation. “666 has the appearance of a large beast with characteristics coming from different animals like a lion, a leopard, a bear, a dragon, etc. It has seven necks, seven heads, with ten horns, as well as seven long thick tails of different shapes.” And remember how Gabriel was affected by it? “It is the image of this beast that persecutes God's people.” It likely has a conceptual thing going on there. Plus it's literally sealed 'at the end of the world', and the Khaos Brigate are already destroying the seals on it according to the last Interlude. It's also stated to appear in Rome because of the Seven hills, and the Vatican is in Rome. Yeah, the Beast of Revelation is something that exists in-universe for DxD, pretty blatantly and its clear thats what this new figure is, no need for the Second Magic my guy. (The Fate imagery is just a visual tool, cause I deslike the designs in DxD since it's world building is barley explored or utilized despite its potential. Like, just look at ExE, some otherworld god's just invade and easily kill Great Red, the plot is a mess.)

Probably the Beast itself, though it does have an actual connection to Nero Claudius Caesar Augustus Germanicus, as they were the reining emperor at the time it was written, and is often referred to as the sixth head. In FGO, Nero is referred to as the Harlot that is associated with the Beast. The Beast of Revelation itself is honestly an interesting figure, especially when interpreted in a universe like the Nasuverse or DxD. “The beast persecutes God's people, and its name is put on the foreheads of its followers. This invisible mark on the forehead or right hand is a stamp of approval from the evil one, and it characterizes those who are against God and trapped in unbelief.” “The second beast, later known as the false prophet, comes 'out of the earth', exercises all the authority of the first beast, forces everyone on earth to worship the first beast.” Really looking forward to how this is used in the story, and I hope we can get a PHO Interlude for the aftermath.

I mean he still has the True Longinus, and I'm pretty sure his Zanpakuto is God kinda like Zangetsu is Yhwach. The spear literally stripped an angel of its Holy Power, an intricate part of their essence, so it can likely help in this case. I highly doubts an Archangel is going to be forced to fall while the spear is around. Plus Jeanne is there with her Flag.

Seven heads, the Beast of Revelations?

It's Canon lore in the Nasuverse that she's illiterate, she also can't do basic arithmetic. To support this idea, Jeanne Alter in FGO is explicitly shown learning to read and write (and I think do math) because she wants to "one-up" her OG self.

Plus the Grail is what supplies the knowledge for Grail Wars (so they can comprehend and be aware of things after their death; like magecraft, technological advancements, or individuals from different time periods or cultures), the Throne of Heros is just where a Heroic Spirits data is stored outside of time for servants to be summoned.

Something Something common belief that Jeanne was a poor uneducated peasant girl (she wasn't, she just had many siblings), resulted in her servant container being affected by that belief, and leading to her being illiterate when summoned.

Was your Fate/Apocrypha story deleted? Like the Sukuna story was?

Part 1 is in 475, Part 2 is in 482 Chapters aren't 1:1, so use the built in chapters, not the story chapters.