So there's enough research on the Internet to make a lot of conclusions as to what Arwen's original role was intended to be.
FOTR
1. Gilraen's Memorial originally had a second part of the scene that ended with Elrond pushing Aragorn to cut things off with Arwen so that she would go to the Undying Lands. This deleted scene ended up in TTT as a flashback.
2. Arwen and Aragorn's "breakup" was originally shot for FOTR, making more sense of Arwen's farewell shot that is still present in the Extended Edition
3. Aragorn tells Galadriel he wants Arwen to go into the West
TTT
1. Arwen's vision in ROTK was originally in the first half of TTT, prompting Arwen to return to Rivendell and set off a chain of events that would send...
2. Arwen and Elrond to Lothlorien, where they confer with Galadriel
3. Arwen and Galadriel have a private scene of some kind
4. Arwen leads troops to Helm's Deep
5. Arwen fights in Helm's Deep
6. Arwen....???
This is where the mystery begins for me. If Arwen traverses across half a continent to help her lover in battle, what would prompt her to...
ROTK
1. Arwen returns to Rivendell from Helm's Deep. In the trailer, there is a scene of her on a bridge as Elrond says he cannot protect her anymore.
2. Arwen drops a book in a library. She is losing her immortality.
3. Arwen is later said to be dying because of Sauron's growing influence on Middle-earth.
Arwen telling Elrond to "reforge the sword" is an offscreen V.O. that appears to be entirely constructed in post. I am guessing that Arwen looking at Narsil is also a pickup.
We also know that Helm's Deep was not the original climax of The Two Towers and Arwen does not appear at the confrontation at Isengard at all. There likely would have been little time in the screenplay to provide much of an explanation as to why Arwen doesn't continue to lead in battle in alliance with Rohan. So the questions I have are:
1. What, if any, explanation would the audience be given as to why Arwen returns to Rivendell? Did she also originally bring Anduril with her in scenes that were abandoned? Is the scene with Elrond in the tent in ROTK a pickup?
2. Would Arwen's plot in ROTK then revolve around her losing her immortality? What was the original incentive for Elrond to reforge the sword?
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I think you might be somewhat on the right track but what if the vision of the child she would have with Aragorn was from Galadriels Mirror in Lorien?
In the Two Towers when we see the Flash Back to the original plot excised from fellowship of the ring What if this was Arwen Leaving for Grey Havens then... That then increases the Love interest for Aragorn and Eowyn. Aragorn thinks about moving on... But she finds another reason to return to Rivendell perhaps because she senses Aragorn is in trouble as he loses the Evenstar at this point the connection between them is broken.
So as Arwen bolts back to Rivendell fearing Aragorn was to lose his life we then see the Balcony scene from the trailer "you have given up your lifes grace I can no longer protect you"
When Aragorn takes the fall off the cliff perhaps Arwen and Aragorn about a good dream and the snogging then cut to the horse waking him up good gag that :)
Elrond accepts that eventually Arwen has made the choice she has made and he takes her to Lorien where the council meeting takes place where Elrond is the one to persuade the Elves to help out and send Haldir. Elrond leaves but Arwen stays in Lorien.
Arwen feels lost about her decision knowing that Aragorn still might die in the near future or if the ring goes to Sauron she will fade quick so she looks into the Mirror of Galadriel when she sees that there is a child she rides back to Rivendell on these tiding of hope that a better future can be found. She also sees the ghosts which she does not understand....
Arwen confronts Elrond about she never told her there was the possibilty of a child.
The Even Star Breaks when Aragorn looks into the Palantir and Arwen begins to Fade this triggers the Re-forge the sword and the research of the paths ofd the dead to change the outcome and the intervention required for the future she saw in Galadriels Miror
That is perhaps my brief take but hey who knows?
(This post was edited by Ronster on Dec 7 2020, 8:56pm)