During an expedition, the Survey Corps come across a human girl who is friendly with the Titans. She's even protected by them. She knows about Eren and made her escape with Eren in her hands. But luckily Eren was released and the girl was no where to be found. They head back to the wall to retreat and come up with a plan to catch her. The girl isn't going down without a fight as she also plans to stop them. Then new dangers come into play... Will the girl and Survey Corps come together and work together to face these threats or... Will this be the end for humanity?

After a recent expedition, Mikasa went missing; whether she even returned alongside her troop was still in question. At the same time, they found a stack of letters hidden in her dorm; all to Eren Jaeger, but never sent. When reading them himself, he finally understands something - something he never, ever did.