Behind Her Blue Flame is centered around Selvaria Bles and an Imperial engineer named Johann, during the Imperial capture of Ghirlandaio at the beginning of the war.

After completing the missions included in the DLC you unlock Ruhm, a longe range and high power weapon used by shocktroopers which combines the power and magazine size of a machinegun and the accuracy of a rifle as used by Selvaria during her last stand at Ghirlandaio. This is much easier than you may think as Selvaria has access to the games two most useful orders, Defense Boost and All Units Defend. These orders make it so even engineer Johann will be able to absorb interception fire and makes Selvaria strong enough to run headlong into walls of defending shocktroopers and heavy gatlings.

Completing all main missions with an A/S allows the player access to the 4th and final bonus mission, in which it is possible to play as Selvaria in her Valkyria form.