Youji Takatsu is a third-year middle schooler in Class 2 at the Eastern Private Defense Academy and a core member of the Basket Army. During summer training at the Fuji Training Facility in August 2026, Trident mercenaries attacked to seize the Regeneratable Artificial Nerve (RAN) experiment, killing numerous classmates and instructors. Surviving the assault, Youji joined fellow survivors to form the Basket Army, dedicated to protecting RAN while evading both Trident and law enforcement due to false public accusations of terrorism.

His personality blends sarcasm and self-awareness, exemplified by his remark: "It seems we have become armed middle school students. How did it come to this?" He occasionally narrates events with a cynical perspective. Interactions showcase his dry humor, such as teasing the energetic Nanami Kanou about her loud voice or engaging in competitive banter with the equally aloof Ann Matsuura.

Youji shares a close childhood friendship with Ann Matsuura; both enrolled in the academy following familial conflicts. Their relationship evolves into a romantic one after the conflict with Trident concludes. In combat, he coordinates with other Basket Army members like Touko Natori and Kazuki Kurobe, utilizing firearms and tactical knowledge gained through the academy's defense program.

Following the Basket Army's success in repelling Trident and clearing their names, Youji continues his life with Ann, transitioning from combat to normalcy.