Miwa Uzuki, who later took the surname Tamashiro after marriage, began life as an orphan; she lost her mother early, and years later her father died, leading to her adoption by the Shiba family. This integration established her deep bonds with Hiroshi Shiba, whom she viewed as a brother, and Hiroshi's younger sister Mayumi, who saw Miwa as both an elder sister and a maternal figure alongside their mother Kikue. Her family ties extended to Professor Shiba, Hiroshi's father. She served as his assistant at his archaeological lab and the Build Base defense facility, where she learned of the ancient Jamatai bell embedded within Hiroshi's body. This artifact granted him cyborg abilities and powered his defense against the Yamatai Kingdom.

During the original conflict, Miwa piloted the Big Shooter aircraft, deploying modular combat components that combined with Hiroshi's cyborg form to create the complete Jeeg robot against Queen Himika's forces. This critical role made her a frequent assassination target for the enemy, as her elimination would prevent Jeeg's formation. The relationship between Miwa and Hiroshi varied across adaptations: the manga depicted cooperative partners with underlying mutual affection, while the anime emphasized friction, portraying Hiroshi as resistant to his duties and Miwa providing moral grounding. A significant subplot involved General Takeru, one of Himika's commanders, who experienced emotional conflict upon encountering Miwa due to her striking resemblance to his deceased wife.

Following Professor Shiba's murder, Miwa's responsibilities grew as she assisted his digitized consciousness, uploaded to the Build Base computer system prior to his death. This digital entity continued to provide strategic guidance to Hiroshi and Miwa.

Decades later, in the sequel series *Kotetsushin Jeeg*, Miwa's life evolved. At the original conflict's conclusion, Queen Himika shot her down, but she escaped Kyushu just before a dimensional barrier sealed the region. Over the next 50 years, she married, had a child, and eventually became grandmother to Tsubaki Tamashiro. Commanding the new Build Base, she oversaw operations against the resurgent Yamatai Kingdom. She maintained a protective watch over Kenji Kusanagi, the new Jeeg pilot, and her granddaughter Tsubaki, who became co-pilot of the Big Shooter, following Miwa's path. The sequel also featured a reunion between Miwa and Hiroshi when he reappeared to aid the new generation in the final battle. Miwa's legacy continued directly through Tsubaki, who inherited her role in supporting Jeeg's operations.