Complete the indicated mission in Attack mode to unlock the corresponding character in Expedition mode.

Annie Leaonhart: Complete "The World The Girl Saw" mission.
Bertolt Hoover: Complete the "At The Edge Of The Forest" mission.
Christa Lenz: Complete the "At The Edge Of The Forest" mission.
Erwin Smith: Complete the "Soldiers Dance" mission.
Hange Zoe: Complete the "Return To Trost District" mission.
Levi: Complete the "Scout Regiment" mission.
Reiner Braun: Complete "The World The Girl Saw" mission.