wait what IS ur descender childe theory? like how does that work?
alright so fair warning i am not the greatest at articulating my thoughts (and i wasn't the person to originally come up with the theory anyways) so if you want a better explanation of the theory, here's a video by Minsleif talking about it
the descender childe theory has actually been around since Fontaine, but has gained more evidence with durin's story quest (yes, a story quest that tartaglia is not even relevant to lol) and some lore drops about the third descender in nod-krai
so in the nod-krai book collection Hymns of the Far North, we learn some information about Saarelainen, the third descender (aka the guy whose remains the Heavenly Principles/the Primordial One/Phanes turned into the Gnoses. This book repeats this information, which we initially learned from Skirk in Masquerade of the Guilty)
but something that people quickly noticed is that the story of Saarelainen is very similar to the story told of a character named Ajax told in the description of the Ballad of the Fjords polearm
also the two people talking at the end of the description are (most likely) a younger Tartaglia and his Father
the name Ajax is also mentioned in a note found in The Narzissenkreuz Ordo, which (combined with the Ballad of the Fjords story) is a big part of why this theory popped up all the way back in Fontaine
so how is tartaglia relevant here? the answer is that his real name is Ajax. In his 3rd Character Story, it's mentioned that he was specifically named after Ajax from the Ballad of the Fjords ("In those days, he was known neither by the names Tartaglia nor "Childe," as the Fatui call him, but as Ajax, named by his father after some hero's tale. He and his father would cut holes open upon frozen lakes before sitting beside them and tending to their fishing lines.")
and, as we learned from Durin's story quest, in Teyvat your name is connected to your fate
additionally, we've learned that things like fairytales are a good way of preserving information even if that information gets deleted from irminsul (and because of that, stories in Teyvat are never just stories). An example of this is Nahida preserving information about Scaramouche with a story of her own.
So. Ajax from the Ballad of the Fjords and Saarelainen, known to be the Third Descender, from the Hymns of the Far North are (most likely) the same person.
Tartaglia, whose name is also Ajax, would be connected to Ajax from the Ballad of the Fjords because names are related to fate.
So Ajax (historical) = Saarelainen (3rd Descender), and named are tied to fate so Ajax (historical) impacts Ajax (Childe/Tartaglia)'s fate. If Ajax (historical) = Saarelainen, that would mean that Saarelainen impacts Tartaglia's fate
and we have already seen that Tartaglia's story connects to things we have heard about Ajax (historical)
Ajax (historical) is said to have sailed a ship into the belly of a great whale, and he fought dragon for seven days.
Something we learn in the Narzissenkreuz questline is that in a story, a dragon is not necessarily an actual dragon
Now, what is it that Tartaglia was up to during the Fontaine Archon Quest?
fighting this fucking thing
additionally, in the note about Ajax from the Narzissenkreuz Ordo, there's the line "...forsake the self and sink into the abyss, and in the abyss, to welcome rebirth as a holy infant." which led Rene to believe that it was possible for an individual from Teyvat to become a Descender (as Descenders aren't inherently from another world). Based on what we know about Saarelainen/historical Ajax, it is most likely that he was originally from Teyvat and became a Descender somehow, possibly in some way connected to The Abyss
There is a character we know who wound up in the Abyss and came out acting different. You could say they experienced something of a "rebirth" in there.
once again it is this fucker
and once again, Tartaglia's story mirrors historical Ajax's, and therefore mirrors Saarelainen's
also, part of Tartaglia's About Dottore voiceline is "Well, come to think of it, if I met another version of myself⦠Hah, we'd have to fight then and there to decide which one of us gets to survive."
Which could mean nothing
i've been yapping for a while now and the linked video articulates information better than i can so uh
TL;DR Tartaglia's fate very much might mirror that of the Third Descender, Saarelainen. If that happens, he will likely become a Descender and also he's kind of fucked. Saarelainen's fate involves self-sacrifice, so Tartaglia may also sacrifice himself in some way.
can you see why i, a person who was already very attached to tartaglia as a character, would intensely fixate on this theory