The strong AoT feelings are back so here come some spoilers (including ones from the manga c: )
Out of everyone I feel like Jean has the most character development in the show. I don't think you can put anything in this show in the trauma layer because they're all traumatized anyways. They become soldiers at a young age. All they see is death and destruction. So that's more of a common trait in this show.
Jean's motives start really selfish tho: 'I wanna be safe in the interior'. Until he can't ignore the passed events anymore and picks a path that goes against his beliefs and maybe even his nature. So we slowly see him going from that kinda weasly brat to a full fleshed adult over the seasons and I like that a lot. He really annoyed me at the start of this too, so this is a character I have grown to love over the span of the series. Especially in this last season where he obviously takes on a more leading role. The moment Floch mentions 'Why don't you go back to being the old Jean' is a turning point as well as a viewer because you're here like "how could he even go back to old Jean?" Bc he can't and this last episode just shows that.
And I know most people would pick Eren as the character with the biggest change, but that is a lie. He's more like a constant in the series. He stays the same over the whole series and only has one goal. At first it seems kill all the titans, but that is not it. His biggest goal is achieving freedom in whatever way possible. He does it by killing the titans at the start until he realizes that there is a whole other world out there that hates them just for who they are. So he would never be free. Hence 'If we kill all our enemies over there, would we finally be free?' is a turning point in the plot as well. That scene symbolizes a lot. This scene was a moment where Armin had achieved his goal as a person: explore and see the ocean. Where Eren just thought of the ocean as freedom, he sees it's not. And that just gets the ball rolling for the rumbling. Eren and Zeke being the 'nature vs nurture' dilemma is a totally valid point here. No normal child kills 2 people at the age of 9. I just have so many feelings about this show and how it's about to end.
Sidera nostra contrahent solem lunamque