The republic of magnolia has been at war with the Gladion empire for nine years. Though it initially suffered devastating losses to the Empire's autonomous mechanized Legion, The Republic has since developed its own autonomous units, called Juggernauts, which are directed remotely by a Handler. While on the surface the public believes the war is being fought between machines, in reality, the Juggernauts are being piloted by humans and all of them are the Eighty-Six, the designation given to the racial minority Colorata of The Republic who originally had equal rights as the dominant Alba race but were persecuted and scapegoated by the racist-led Alba government to the point the Colorata were considered not human, not allowed to have names and forced to live in internment camps in the Eighty-Sixth Sector while being forced to fight in the Republic's war with the Empire to restore their family's civic rights.

Vladilena "Lena" Milizé is an Alba noble of Major rank in the Republic's Military who is assigned as a Handler of the elite Spearhead Squadron comprised of seasoned Processors who have earned names. Led by their field commander and squad leader, Shinei "Undertaker" Nouzen, the Spearhead Squadron are infamous due to many Handlers who have commanded the squad having their psyche broken down and some even committed suicide. As Lena gets to know Shinei and the rest of the Spearhead squadron, she becomes sympathetic to his people's plight and tries to help them. At same time, Lena and Shinei learn a dark secret: the Republic and the war with the Empire is not what it seems on the surface.

16-years-old Vladilena "Lena" Milize is a Major serving in the military of the Republic of San Magnolia, a country that prides itself as the first modern democracy in the world, and has been locked in a war against the remnants of the destroyed Giadian Empire for the past 9 years. However, by this point in the war, the ideals of equality the Republic upheld were mere empty words. The country is led by a racial supremacist government who stripped the rights of the colored citizens (Colorata) and condemned them outside the fortifications of the country, a region known as the Eighty-Sixth Sector and its inhabitants, considered as sub-humans, are referred to as the Eighty-Six. The young men and women of the Eighty-Six are forced by the Republic government to fight their war against the Empire's advanced autonomous drone army, the Legion, by piloting makeshift "drones" known as Juggernauts in order to liberate their families from the Eighty-Sixth Sector and restore their citizenship.

Witnessing this atrocity personally when she was younger, Lena could not let this injustice be ignored any longer, and with her fervid sense of justice she tried her hardest to help the Eighty-Six in the war before it was expected to end in the next two years due to the lifespan of the Legion's central processors. To her surprise, she was assigned as the Handler of an elite squadron of name-bearing Eighty-Six known as the Spearhead Squadron, led by the ominous Undertaker that drove his Handlers insane. She is repeatedly encouraged not to take the job by her closest friend, Henrietta von Penrose. Annette suggested that Lena instead transfer to the research division to work alongside her, as "former military personnel" would not be a good occupation to put on her resume once the war was over.

Lena remained steadfast in her ideals and took the position of Spearhead's handler.

After exchanging words with Undertaker over the Para-RAID, she concluded he wasn't as dangerous as the rumors say and her suspicion of him faded away. By then, she was comfortable enough to routinely converse with the squadron's members every night. In spite of her efforts to close the gap between her and her squadron's Processors, the clear line of the oppressor and the oppressed still remained and earned her more than a few cold comments on her good-natured yet naïve behavior from the squadron's members. Despite that, Lena hadn't given up and continued to lend an honest helping hand to the squadron's battles against the Legion. This cold and distant relationship between her and the squadron would last until she was unable to prevent the death of Kirschblüte, one of the most active members when it came to their nightly talks. A hurtful rebuke from Laughing Fox finally made her realize her own self-centered, hypocritical manner of treating the Eighty-Six, to the point she had never even asked for their real names.

She nervously reconnected with Undertaker later that night, apologizing for her behavior and requesting for the names of the squadron's members. Sensing that Lena was eager to prove herself once more to the squadron, he gave her a chance and introduced his comrades' names to Lena one by one, also telling her about his promise to carry the tags of his fallen comrades. With his help, she would manage to repair their relationship and set a true foundation for their interactions moving forward. Undertaker would eventually introduce himself as Shinei Nouzen, to which Lena would ask if he was related to a Processor by the Personal Name of Dullahan—Shourei Nouzen—who saved her when she was taken to the Eighty-Sixth Sector by her father six years ago. He confirmed that Shourei was his brother and told her of his death five years ago. He admits to Lena that he does not have any plans once he was discharged, only that his current goal was to search for his brother. Lena was confused by what he had meant, but Shin simply deflected, not telling her what he truly meant.

While overseeing another sortie, Shin abruptly directed her to cut resonance mid-battle. Not comprehending the meaning behind the message, Lena protested his suggestion, only to end up having a panic attack due to the horrifying macabre noises coming from the Legion. In the evening, to Shin's surprise, Lena gathered the strength to resonate with Shin once again. She discovered the truth about the sounds—the Legion were taking hold of the dead Processors' brains to augment their lifespans and thus retaining the ego the Processors had moments before their deaths. The Legion that had assimilated the damaged brains of the dead were referred to as Black Sheep, and those with undamaged brains were referred to as Shepherds.