Azumi Kagamihara faced a life-threatening childhood illness that brought her to the verge of death. Her survival required medical intervention from the Blue World, one of five alternate dimensions connected to Earth through spatial rifts. This treatment carried the condition that she form a combat partnership with Rigel, a humanoid battle dress unit from the Blue World, to fight inter-dimensional threats. The arrangement granted Azumi an extended lifespan but tied her to ongoing conflict through this bond. Her near-death experience profoundly shaped her personality, resulting in a reserved, introverted demeanor. She often appeared mature for her age and spoke sparingly, yet possessed an exceptionally strong attachment to staying alive due to her brush with mortality, making this will to survive a defining aspect of her character.

Rigel was initially programmed by the Blue World to monitor Azumi and ensure her cooperation, presenting as a companion. Over time, Rigel developed genuine emotions and loyalty, shifting her primary mission to protecting Azumi above all else, even if it meant defying her original directives. This evolution formed the core of their relationship.

As part of their agreement, Azumi and Rigel were assigned to Fujimisaki Academy, a specialized institution established to train human-Z/X partnerships following a fragile peace treaty between the five worlds and Earth. During orientation, the academy came under attack by the Inerma, extradimensional entities that feed on world destruction. Amid the chaos, Azumi joined four other students—Ena Soranokawa, Shuri Kijino, Matoi Shinonome, and Yuni Tsukigata—and their respective Z/X partners. Together, they accessed the academy's Drive Shaft defense facility and engaged the invaders, though they required rescue by the Student Council. This event led to their formation as an unofficial sixth academy team.

Designated Team E, the group occupied the lowest rank among the academy's squads. Consequently, they were assigned to dilapidated dormitory facilities away from the main campus. Their instructor, Ira, exhibited a volatile teaching style fluctuating between supportive guidance and extreme physical demands. Azumi initially struggled with interpersonal connections due to her reserved nature and survival focus. However, through shared experiences—including rigorous training, a summer vacation trip featuring beach activities and fireworks, and repeated confrontations with the Inerma—she gradually developed bonds with her teammates. These interactions helped her transition from a solitary focus on self-preservation toward recognizing the value of teamwork and mutual reliance.

Key team conflicts, particularly the initial friction between Matoi and Shuri and Yuni's reluctance to engage fully, provided contexts for Azumi to observe and participate in conflict resolution. Her partnership with Rigel deepened beyond a transactional arrangement into one characterized by mutual care and sacrifice. During critical battles against the Inerma, especially a climactic orbital confrontation requiring coordinated efforts from all five worlds, Azumi's motivations expanded. She began fighting not solely for her own survival, but for the protection of her teammates and the preservation of their shared peace. This shift marked her primary character development, moving from isolation toward integration within a supportive community.