Board Thread:Questions and Answers/@comment-30771283-20171113094245/@comment-1327106-20171113161735

First you need to beat Chapter 3. After that's done, you go back into the game so you're at your base (or you can go directly into Survey Missions from the Main Menu if you don't care about using your chosen difficulty setting). You'll then need talk to the guy who lets you do the optional Survey Missions.

Now comes the stinky part.

You need to complete 80% of all missions in each Survey Mission zone in order to unlock one epilogue mission. You start with Southern Region 1st Survey, so you'll need 80% of that done for your first epilogue mission. While you're partway through that, Interior Defensive Area will unlock, so you'll see your next zone ahead of time, if for some reason you feel you want to skip around. There are six Survey Mission zones, but you only get epilogue unlocks for the first five.

If you really like this game, or want to play a lot with someone who is not Eren/Mikasa/Armin/Levi, you'll probably be fine going through the optional Survey Missions. Jean is one of my favorite characters, so I actually had more fun with the Survey Missions than the main game, because I got to play Jean all the time and pretend he's a more important character than he is. But that's probably not true for most people. ;)  I've heard complaints on forums from people who got tired of it way before they finished unlocking all the epilogue missions.

I think most people unlock the first one or two, but the later Survey Missions get more difficult than the main game and I think that's when people start to slow down and get bored/frustrated.