I always thought this letters would be a nice idea and finally decided to write some of them.
Well, actually I already have those which I wanted to write ready in German, but I realized it is really hard to translate letters, even more as I'm translating from and not to my native tongue.
Therefore I apologize in advance should there be some mistakes disrupting the reading or should it take me too long to post the next chapter.
Probably I'm just struggling trying to keep the mistakes to a minimum. Usually I would ask a friend to beta this for me, but I would spoiler her and I don't want to do that. (Should you by any chance be reading this, please, stop right here!) So, yes, this is not spoiler-free unless you have seen most of the anime.

1: Petra to Levi

He stared at the piece of paper in his hand, hesitant to rip it open. It was labelled in a clear, fluid way with nothing more than his name. No title, no decoration or squiggle. Just his name.
It had been obvious that Petra would be one of those to write such a letter. A farewell letter. Prior to each and every expedition. Again and again.
As if knowing the high risk to die was not already enough, as if there was nothing more important than leaving words for those left behind, making them aware of all they had lost once again.
There was no obligation to, but most soldiers would advise especially young ones to write these. He thought it to be sheer torture. With an expedition ahead people should concentrate on preparations not on thinking what to leave behind should they not return. It did not bring any inward peace, just the pressing knowledge that it was not that unlikely to happen. Making it clear again and again what could be lost. Even if he had wanted to he did not have the strength to do it. Not time and again.
But Petra's letter was of recent date. The date stamp sitting so wrongly in the lower right corner bore the date one day before their ride outside the walls. One damn day. And he knew far too well that she had done the same last time and every single time before. She always wrote new letters and most likely even more each time.
He glanced towards his desk where four more letters lay carefully sealed and inscribed. They had handed him the ones to his other squad members as well. Such irony.
Levi leaned back shortly then sat up, putting his own letter aside and reaching for the other ones. He sorted out Eren's and let if fall next to his own. Then he took a moment to simply look at the three other names in the candle's flickering light. Erd. Günther. Auruo.
With a deep sigh he stood and took a few steps towards his fireplace. He felt old, his movements weak and tired and his thoughts weren't in any better shape. His gaze went to the crackling flames and for a brief moment he tried not to think of anything, but pictures glowed in his mind making him try to push them away quickly.
He shut his eyes tightly and rubbed his forehead with his free hand. All of them ... they just kept on disappearing ...
He opened his eyes again, extended his right hand and threw the letters into the flames with a quick motion, before he turned and went back to his desk. Petra's last words would never reach them and he surely did not want to read them. That was a private matter.
He sank back on his chair and looked at his own letter again. Did he really want to read it? Did he really want to know what she had to say?
With a sigh he jerkily broke the seal. Just as he expected a lot of lines appeared, Petra did not make it short.

Levi,

I know you won't approve of me addressing you without your title, but I want this letter to reach not my superior, but a person who I have come to see as a friend and respect very highly.
I know you always try to seem unimpressed, but I can see in your eyes that all the deaths hurt you just as much as everyone else, that you miss the people and probably ask yourself if you could have done anything to prevent them from leaving.
You're making your own life harder than you would ever admit and I'm not sure, whether I won't make it worse with these lines. But I wanted to thank you. For being there for your subordinates, for taking care of them even if they themselves aren't aware of it.
I could not wish any more of a superior and I'm sure I'm not the only one to think that way. Those who are lucky enough to really get to know you will appreciate it. Don't take those rumours about you being cold-hearted and unapproachable to heart. You are a warm-hearted and good human being and I'm glad and proud to have worked with you.
Thank you for the first weeks as well. Perhaps it was too unimportant for you to even remember, but when I was new to the legion you taught me to stay calm and told me everything was under control, the risk calculable as long as we kept sight of the bigger picture.
You were right. Even if I was not able to really stay calm all the time I tried to take it to heart and it made things easier for me.
Whatever people may say, stay the way you are, one day they will for sure understand.

Thank you for everything and, please, take care.

Petra

Levi let his arm fall down slowly and leaned back while closing his eyes. A softly murmured "Petra ..." escaped his lips with another sigh. She had seen more in him than what was actually there, that much he was sure of and she had worried about the wrong things, but...
He smiled sadly, folded her letter neatly and put it almost carefully into his desk drawer where two others were placed already.
He would miss her.