Spoiler alert: This article contains spoilers for Season 4, Episode 28 of the anime Attack on Titan.
To describe Attack on Titan as a gnarly anime/manga would be an understatement. The series has a simple yet horrifying premise: humanity is plagued by giants in the world who feed on people.
The main protagonist of the series, Eren Yeager, has undergone some intense changes throughout the series, but fans were shocked to see what he did to his body: gouging out his own eye and cutting off his leg for seemingly no reason. So why did he do it?
Why did Eren cut off his leg?
While Falco was talking to a brooding man with a bandaged eye who is missing a leg, viewers weren't entirely sure who the individual was. However, once focus shifted to his eye, it became clear who he was: Eren Yeager.
Eren has an unshaken resolve to destroy all of the Titans in the world ever since seeing his mother eaten alive by one of the monsters after his hometown in the Shiganshina District had its wall breached. Once the beasts invaded, many of its citizens were brutalized and consumed, Eren's mom included.
Since Eren Yeager is part of the Subjects of Ymir bloodline, he is one of the few descendants who is able to transform into a Titan, an ability which was given to him in the form of a serum administered to him by his father, Grisha Yeager. To defeat the monsters, Eren uses these Titan skills, which — combined with his intellect and military training, plus accumulation of other abilities through consumption of other beings/enemies — makes him a formidable hero.
So why would he compromise his body if his goal is to eradicate the world of Titans? Well, that's because a larger part of Eren's plan required him to not be discovered at Marley. In order to perfect that disguise, he gouged out one of his eyes and cut off his left leg so he could play the part of someone else.
His disguise allowed him to seamlessly blend in with Marley's Eldian soldiers, and he also needed to buy some more time to discuss matters with Zeke while in Marley.
So, in order to look like an everyday soldier and not the Titan-killing machine that is Eren Yeager, he gave himself some war wounds so he could shack up in a Marley hospital.
It's not like anyone's going to argue with a guy who lost an eye and leg for the cause, you know?
Can Eren heal his leg and eye?
Because of his abilities, Eren is able to regrow his leg and eyes, something that folks who read the manga already know.
In fact, when he's outed as the "rebel" who threatens the peace of the Marley nation, Eren actually heals his leg right in front of Reiner in a crazy scene that's almost as hard to forget as the one where he injures himself in the first place.
It's here that Eren meets Falco and befriends the young boy and gets him to send letters to members of his team under the guise that they are correspondence intended for his family.