The game takes place during the Second Europan War. Gallian Army Squad 422, also known as "The Nameless", are a penal military unit composed of criminals, foreign deserters, and military offenders whose real names are erased from the records and thereon officially referred to by numbers. Ordered by the Gallian military to perform the most dangerous missions that the Regular Army and Militia will not do, they are nevertheless up to the task, exemplified by their motto, Altaha Abilia, meaning "Always Ready." The three main characters are No.7 Kurt Irving, an army officer falsely accused of treason who wishes to redeem himself; Ace No.1 Imca, a female Darcsen heavy weapons specialist who seeks revenge against the Valkyria who destroyed her home; and No.13 Riela Marcellis, a seemingly jinxed young woman who is unknowingly a Valkyria herself. Together with their fellow squad members, these three are tasked to fight against a mysterious, primarily Darcsen Imperial unit known as Calamity Raven.

As the Nameless officially do not exist, the upper echelons of the Gallian Army exploit the concept of plausible deniability in order to send them on missions that would otherwise make Gallia lose face in the war. While at times this works to their advantage, such as a successful incursion into Imperial territory, other orders cause certain members of the 422nd great distress. One such member, Gusurg, becomes so enraged that he abandons his post and defects into the ranks of Calamity Raven, attached to the ideal of Darcsen independence proposed by their leader, Dahau. At the same time, elements within Gallian Army Command move to erase the Nameless in order to protect their own interests. Hounded by both allies and enemies, and combined with the presence of a traitor within their ranks, the 422nd desperately move to keep themselves alive while at the same time fight to help the Gallian war effort. This continues until the Nameless's commanding officer, Ramsey Crowe, who had been kept under house arrest, is escorted to the capital city of Randgriz in order to present evidence exonerating the weary soldiers and expose the real traitor, the Gallian general who had accused Kurt of treason.