Disclaimer: Naturally none of the mentioned characters, nor the ideas behind them belong to me, but J.K. Rowling. If anyone else has done the same thing, however, I haven't read it and thus I'm not stealing it from them.
Note: What happened is that I thought about how Sirius must have felt in Azkaban and then I just started writing the letters. Their will be mentions of an established relationship between Sirius and Remus, as well as canonical character death and angst, aka: James and Lily died.
Dear Moony,
It's odd what things you remember when you only really have yourself for company, since it turns out Dementors don't make good drinking mates. What I remembered is the time you talked about the inhumanity of our court and justice system. And I also remember not giving a shit because, sod it, dark wizards don't deserve any better.
So. Very belatedly telling you, I'm starting to see your point.
I don't really see many of the other people here, but the worst are the ones that don't know the truth. They smile. They approve.
I think it's even worse than the way the people I actually care about looked at me.
And I just want to yell that it wasn't me, that I didn't kill them! Only, it was me. It's my fault they're dead. I don't deserve any better. I just wish Wormtail were here, too.
- Pa… Sirius