I've always really loved how Geto's trauma has been portrayed. His weight loss is a small detail that I love even though it's sad and besides that his messy, unruly hair (even in scenes where he had his hair tied in a bun it still looked unkempt) and the way he didn't even wear his uniform properly anymore... :( These little details make his story so sad; he didn't have the motivation anymore to do even the simplest of things, he couldn't even bring it in himself to look out together. This is something that is so important to show when you're portraying depression and trauma in media and Gege (and Mappa) did it perfectly.
For anime onlys this episode was really important. All they know about Geto is him being an antagonist from the movie and it's important for them to see exactly what his character was like. He was empathetic, he was kind, he was caring. But he's also the one who suffered the most from being a jujutsu sorcerer. His cursed technique is the hardest and the shittiest. It's literally described as “the taste of a cursed spirit that no one else knows... Like swallowing whole a cloth that was used to wipe up vomit”. No one could understand what Geto went through with his cursed technique nor the amount of pain he undertook. And after suffering so much, after going through so much pian both mentally and physically, after enduring his friends dying just to protect humans, seeing non-sorcerers mistreat sorcerers in such a horrible way, Geto just snapped. And that's how he just started away from his initial ideals; he just couldn't live in a world like this anymore.
And this is when that quote comes: “its just that in a world like this, I couldn't laugh from the bottom of my heart”
Geto Suguru I want to give you a big hug :(( I love you so much