In the begining he is a cheerful kid that never backs down, he keeps moving forward to achieve his desire, freedom, to kill all titans and go beyond the walls, see the ocean, the outside world.

Reaching the sea he realizes who his true enemies are and that the world outside isn't what he imagined, he wants to destroy it all. He sees the future himself when kissing Historia's hand, he sees the Rumbling, the future where he kills 80% of humanity and is then stopped by Mikasa, he is broken, disappointed, angry, angry at his enemies but mainly angry at his own fate, a walking existencial crisis.

He tries over and over to alter fate, to not have his future memories come true, but he of course fails. He sees good in his enemies but he has to keep going forward, because of his hatred and his wish for freedom, that he knows he will never achieve. Why not give up then? Why go through with the Rumbling if he knew he will fail? Because he couldn't, he couldn't give up, he had to do exactly what was destined for him, he was fueled by a great rage, he had to fight, he had to keep moving forward, that is fate.

But Eren cannot cope with that, he is utterly shattered by the reality, the reality that he could never have what he truly wanted, his freedom. Eren, same as Ymir (they are very similiar to eachother) is a very selfish person, he doesn't care about humans or Eldians, he didn't want to alter fate to save any of them, all he cares about is his freedom, he is an idiot, as he puts it, that achieved great power that in turn destroyed him and caused great suffering to everyone around him, and in the end it didn't even matter.

When Armin asks if what Eren did was truly needed, Eren answers that he tried to alter fate, but everything is already destined and set in stone. Eren didn't know exactly how he will be stopped, only that Mikasa will have something to do with it, in the end Eren decided to make a hero out of Armin, Mikasa and the alliance, presumably to at least make peace with humans, but of course war is inevitable. But peace wasn't Eren's goal anyway, it was freedom. In a sense I think it seems like lot of the cast misinterprets Eren's character, in the end they see him as a suicidal idiotic hero that united the world for a tiny bit of history, but he definitely wasn't that, he was destined to be that, but he never wanted to be that, he wanted freedom but knew he could never achieve it.

When Armin hugs Eren for the last time he isn't thanking him for causing a genocide, he feels partly guilty for Eren's actions, for his fate and for the fate of the world. He is thanking him for being his friend, for all the good memories they had and for the struggles Eren went through, he is comforting Eren, making peace with his dying friend, even if he may never forgive him for what he did. Armin has a very big heart, but one could say he's an idiot just like Eren, they are similiar in a sense, two idiotic friends that went on two different paths. It is questionable whether the cast fully understood Eren in the end, my guess is no, I don't blame them, Eren is such a complex character with so many layers. But the one word that would probably describe him the best is "fool".

Eren realizes what horrible things he has done, seeing Ramzi and all the blood he spilled (will spill), but I personally think that in the end he cares more about his freedom than the people he hurt, it seems to me that what hurts him the most is the freedom he could never have, rather than the lives he took, I could be wrong though. Athough at the end it is hinted that Eren reincarnated as a bird, so he might have gotten his wish for freedom granted in the end afterall...

?happy ending for Eren? Anyones guess.

The story briliantly shows how no matter what happens, war never changes and the cycle of hatred continues and there is nothing that can stop it, not even the sacrifices Eren together with Ymir and all our cast made, be it the sacrifice of freedom or sacrifice of lives. Even if Eren succeeded at eradicating all of humanity, nothing would change, the titan curse would still exist and Eldians would eventually fight amongst eachother in a civil war just like the humans, it is inevitable.

It might also be hinted in the end that the titans weren't even eradicated, a kid finds the tree Eren is buried under and the tree looks the exact same as the one Ymir found. But even if titans were truly eradicated, it doesn't change anything, war and the cycle of hatred will continue forever regardless, until all humans (and Eldians) die.

It is a very depressing ending, but a very realistic and poetic one, it teaches us how hatred, war and suffering will never stop, how the cycle of hatred is un-ending, it also shows us how mindwrecking knowing one's fate is and how dangerous it is to hold unwarranted power even for a kid that wanted nothing more than to be free of suffering and confinement. It tells us that the greatest enemy of man is himself, his ego, his narcisism, his fear of inevitable void, his pursuit of meaning or as Ernest Becker puts it; every man's need to deny death. The story also tells us we shouldn't blindly follow our leaders and authority nor our bloodline, race... We should question everything, be prepared, not hate and not hurt others, be educated, not be bigoted, see the perspective of others, feel empathy, accept death, find a meaning and perhaps it teaches us to forgive.

And Armin's & Zeke's conversation shows us that in the end, through all of the inevitable un-ending misfortune, suffering and death, the true meaning of life are the fleeting moments of happiness we experience (and also multiplying lmao).