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I love the idea of determinism in Eren's character, as someone with a complicated relationship to linearity. Eren desires freedom, but in AoT the future is certain & unchangeable which seems opposite to freedom, but instead of being strung along he charges headfirst into it.
As the famous "suicidal bastard" who always charges ahead into danger, the "Attack Titan" who always charges ahead for freedom, he moves forward with everything he has to reach the future that he was destined, the reason he was born.
AoT says both that there is a purpose to anyone being born, as well as that being born is itself a purpose, but every person has a unique role to fill. The future Eren sees isn't a greater force controlling him, it's his own creation, as a result of who he is at his deepest core.
When Eren confirmed that "the future doesn't change" what he really confirmed was he will never change. Even when he has doubts, or is conflicted, the future he sees has already accounted for that. The future only becomes tangible after every test of who he is has been accounted.
All of Eren's internal conflicts and emotional challenges are really him confronting his own true self. This might be a little too abstract to understand what I mean, but look at it this way: If Eren sees his own future and decides to change it, wouldn't the future also change?
The answer is no, not because he isn't in control of his own free will, but because if he sees the future, he also sees the future where he already has questioned himself, has doubted and resisted, and the resulting "future" he sees is what is left after all that, his true self.
This asks us whether Eren's freedom actually came from seeing his own life's path, seeing the person he is but still have yet to become, & instead of denying it & resisting it, comes to accept himself & who he was destined to be, whether it's cruel, beautiful, a god or a devil.
I think the conclusion of Eren's story is a seriously powerful way to use ambiguity, it doesn't tell you how to feel one way or another because it has pieces of everything. Eren simply is, but it's up to us and the characters to make up our own feelings and actions for ourselves.
Eren throughout post-timeskip is really one big deconstruction of his character going back to the source step by step. Pre-ts was the thesis of his character, post-ts started with antithesis, & it ends with synthesis, two conflicting forces existing as one https://twitter.com/ColdCriti/status/1381700991435862016
Another reflection of that duality within him is the two sides I mentioned: the "suicidal bastard who charges into certain death" & "the attack titan who charges forth for freedom". Both who he is as a person & his bestowed purpose both refer to the same thing, moving forward.
And in the end of the story, Eren did know he was going to die, yet still moved forward, literally charging forth into certain death like a "suicidal bastard" while fulfilling the "Attack Titan" mission of freedom passed on by Kruger at the same time.
This is I think a crucial part to understand: Eren didn't "plan" to die, he just knew he would, and did it anyway. If it was meant to be Eren would've flattened the world completely, because that was his mission to save Eldia, which he must fulfill even if he dies, & even after.
He had no choice but to accept the outcome as inevitable, but he saw the potential in it, in his friends who would go on living & continue their fight. It was the result of all their wills colliding & in Survey Corps spirit Eren left it up to his friends to give his death meaning
