Miwa Uzuki operates as a key defender against the Jamatai Kingdom, initially assisting Professor Shiba before his death. Orphaned young after her mother's departure and her father's subsequent passing, she was adopted into the Shiba household. There, she formed a sibling-like bond with Hiroshi Shiba and a nurturing relationship with his younger sister Mayumi, who sees her as an elder sister. Hiroshi's mother, Kikue Shiba, provides maternal care, solidifying Miwa's place within the family.

Her core duty is piloting the Big Shooter aircraft, delivering modular components that allow the cyborg Hiroshi to assemble the titular combat unit. This role demands precise coordination during missions to deploy limbs, specialized weaponry, or armor upgrades under fire. Her dynamic with Hiroshi varies across adaptations: the manga presents them as a cohesive team with little friction, while the anime introduces interpersonal tension, depicting Miwa as a grounding force countering his initial arrogance and reluctance toward his duties.

Her past intersects with antagonists when General Takeru, a revived commander from ancient Jamatai, mistakes her for his deceased wife due to their resemblance. This connection sparks temporary conflict but ultimately strengthens her loyalty to the Shiba cause. Her operational importance makes her a recurring target for adversaries aiming to cripple defenses by eliminating the Big Shooter's pilot.

Decades later, known as Miwa Tamashiro after marriage, she was critically wounded by Queen Himika during the original conflict's climax. Ejected from Kyushu just before a dimensional barrier sealed the region, she was separated from Hiroshi. Over the next 50 years, she married, raised a child, and became grandmother to Tsubaki Tamashiro. When hostilities resume, she assumes command of the new Build Base facility, directing operations against the resurgent Jamatai threat and mentoring the next generation, including her granddaughter Tsubaki, who now pilots the Big Shooter.