Ann Matsuura, daughter of a down-on-his-luck rockstar and a foreign potter—both staunch pacifists—left home after a falling out with her family. Seeking distance from her parents, she enrolled in the Eastern Private Defense Academy, joining Class 2 alongside her childhood friend Youji Takatsu. She generally found satisfaction in academy life despite the rift.

On August 1, 2026, during her class's final summer training day, the mercenary company Trident attacked to seize the Regeneratable Artificial Nerve (RAN) from scientist Tomonori Takizawa, who intended it for Class 2's instructor, Kimiko Kamiya. Most of Ann's classmates perished, but she survived with a small group. Branded publicly as terrorists during their escape from Trident's pursuit, they named themselves the Basket Army to signify their unity and mission.

Within the Basket Army, Ann served as a skilled markswoman. Her expertise shone in late June 2026 during a protracted sniper duel against Trident operative Apache in the forests near Fuji Training Grounds. Ann employed tactical ingenuity, constructing a decoy from crossed sticks, a poncho, and a helmet. This successfully lured Apache into revealing her position, allowing Ann to wound the operative in the shoulder and force a retreat. Ann continued refining such decoy strategies for future advantages.

The Basket Army ultimately prevented Trident from acquiring RAN and cleared their names of the terrorism accusations. Following these events, Ann entered a romantic relationship with Youji Takatsu.