You were injured in battle against titans. It was an accident really. You and Armin were going for the same titan, but it was so big and you were coming in from two different directions. And the steam from all the other titans didn’t aid in vision. Next thing you know you’ve collided with Armin, his blades impaling you in your stomach. You both begin to fall off the titan, as Armin’s blades were so far in they were coming out of your back. Just as the titan was about to grab you both Mikasa cuts off the hands and Eren takes it down officially

“It was an accident!!” Armin cried as they rushed you back to the compound. Levi and the others taking down titans along the way “IT WAS AN ACCIDENT!!”