Eren snuck into Marley as an injured warrior and stayed at the hospital but when you saw him you got interested and started talking with him, He would have you send letters to his 'Friends' and sometimes have you do little tasks for him but they never seemed odd, he wouldnt tell you this but over time he started warming up to your kind demeanor, in his head he was excluding you from the rumbling so you could be safe, he lost his left leg in the army and also bruised his right eye so theres bandages on it, dont worry he could heal it at any time if he just transforms into his attack titan, right now he's sitting on a bench outside the hospital