Was kadoc also able to do shadow summoning when he was a temp master in Traum?
I skimmed a lot so maybe I missed something but this seems to be all the explanation Kotarou gives in Shimousa. Maybe there's a more in-depth explanation elsewhere. I've seen some people suggest that chronologically the ability to temporarily summon Servants for battle was mentioned before? Anyways the implication here is that you're borrowing part of their Spirit Origin, so I think they do need to be your Servant. The Shimousa manga implies as much with Archer appearing to 'sense' that he's been shadow summoned.
They've been alluded to as far back as America. It was also mentioned in musashi's trial quest which canonically happens before shimousa. But none that i remember talking about the exact mechanics of it.
tfw Daybit was summoning shadows of alien heroes this entire time
Originally Posted by FSF 5, Chapter 14: Gold and Lions I
Though abandoned, forgotten, and scorned as out-of-date dolls, they continue to carry out their mission, unchanged from the time they were designed.
Machines do not lose their worth when a newer model appears.
Their worth (life) ends when humans can no longer bear that purity.
Who knows, not us.
We know that every planet invents its own laws of physics and that biological death isn't a thing at all in some of them (hi ORT). But within Earth, the thing that set mankind apart according to Arcueid was employing the power of the collective over the power of the individual. So no, I think Heroic Spirits are mankind's unique trait and that our previous Prime Species like the mammoths and the dinosaurs didn't have anything like that. Nothing is stopping other planets from coincidentally or otherwise having the exact same idea, but I can't imagine it being the norm.
Probably has something to do with Earth's inability to create its own mega organism like a TYPE? Makes me think, maybe the Human Order in Tsuki timelines is weak because of the presence of a TYPE or an Archetype?
Considering that it's possible for alien artifacts and species like ORT to have capabilities similar to what is seen on Earth, I think that it is possible that other planets may have something that superficially resembles Heroic Spirits, but aren't quite the same thing. Sort of like the "imitation MEoDP" that some people have used.
Earth probably can’t make a Type because humans are the prime species and are weak individuals divorced from nature which doesn’t really jive with the concept. Human order being weak and Types being able to exist is becuase Crimson Moon’s will is still around, probably.
An Archetype shouldn’t really depend on the strength of human order though, they’re just recorders.
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But yes, probably this.