Attack on Titan: No Regrets Vol. 2 (manga)

Erwin's political enemies have hired Levi and his crew to take back some incriminating documents. Their reward: the right to live a proud life above ground, in the royal capital. But deep in Titan territory, it's going to be tough to break formation and steal from a squad leader, and Levi still insists on killing the man who humiliated him after the mission is complete. Of course, beyond the walls anything can happen, and a sudden change in Levi's fortunes will force him to face the greatest regret in his life...