- The Little Prince. He denies it, but he doesn't seem to know himself.
- Jesus: There's Christian Apocrypha all over Requiem, the Wandering Jew, Longinus, the nail that pierced Christ, Galahad (Alter), etc.
- His catalyst for being summoned was Erice being pierced by (a shadow of) the Lance of Longinus, in the same place Jesus was pierced by it.
- The original Voyager Spacecraft. Armstrong's mission was "56 years ago" in story, making it 2025 if they hadn't changed it. The year Nasa says that Voyager is scheduled to go offline.
- A combination of the three.
Voyager 1 was dying. It's 2025, 56 years after the Moon Landing as mentioned in story. It's solar batteries were running out, just like NASA said it would in 2025.
Near the end, it gained a soul. It asked...a question. A prayer. Is anyone out there? Will anyone be my friend?
And there alone in the Outer Dark it was answered by Someone. They're not going to say that Someone's Name. But spoiler alert, it's Jesus. He heals Voyager, and tells him that there's other people who need help. They're trapped in their bodies after making the wrong wish. Physical Immortality was never the point of the Holy Grail; that was an unwanted side-effect. If things stay this way, they'll suffer in ways nobody can imagine. Voyager says he'll help, and He sends Voyager back to Earth.
Now, when a Servant, which Voyager is now, gets boosted by a strong enough Authority, they gain aspects of that Authority. (See, BB becoming Nyarlathotep, or Sieg becoming Fafnir) Being boosted by....the Messiah, Voyager gets a Phantom closely resembling that Power; the Messianic Archetype known as The Little Prince.
Remember, in the Little Prince, the only way he could go back home was for his body to be killed by the snake. Voyager finds that aspect of his Phantom a little scary. Normally this phantom would be way too weak to be of any help, but again....powered by the actual Messiah.
And yes. It's gotta be Jesus. There's too much Christian Apocrypha in Requiem to be anyone else. The Wandering Jew, The Flying Dutchman, Longinus, Kundry, Galahad, the Sword of King David, Stigmata, the Nails of the Cross, etc. etc. etc.
- The epilogue of volume 1 confirm him to be the original Voyager Spacecraft.
- And the Fate/Grand Order collab confirms that he has aspects of the Little Prince because that's how Erice saw him.
- The epilogue of volume 1 confirm him to be the original Voyager Spacecraft.
- A "Requiem" is a song or prayer for the souls of the dead to be at peace.
- Fate/Grand Order actually agrees with this. The Atlantis Lostbelt is stated to be been pruned because under the Greek gods' control, humanity has essentially done all it can and cannot grow anymore. Adele and Makarios, who live in Olympus, are 10,000 years old despite looking like teenagers, and are so bored by life they want to die.
- Upon finishing Requiem's Holy Grail War; he's going to carry their souls with him on his journey. And then, after a million billion trillion years, he'll land on a new planet (just like his final Ascension in FGO shows). He'll use his Rhongomyniad Aspect to attach a new texture for humanity. Perhaps it wouldn't be enough for normal humans; but souls with Holy Grails in their hearts would be able to adapt and thrive to it.
As for under what name she would go by after she reveals her True Name, most likely Yurlungur because that is the one Shin Megami Tensei uses.
