Miwa Tamashiro, originally Miwa Uzuki, piloted the original Big Shooter fifty years before the sequel series. She operated alongside Hiroshi Shiba, the original Jeeg pilot, delivering crucial combat components during the conflict against the Great Jama Kingdom. Her support proved critical to Hiroshi's battles against Queen Himika's Haniwa Phantom Gods. A pivotal confrontation with Himika resulted in her being shot down and ejected from the Kyushu region just as the dimensional "zone" barrier sealed the area. This trapped Hiroshi inside, preventing their reunion for decades.

Fifty years later, now bearing the surname Tamashiro, she assumed command of the newly established Build Base following signs of the Jama Empire's resurgence. By this time, she was grandmother to Tsubaki Tamashiro, a key figure of the new generation. She had maintained protective oversight throughout Kenji Kusanagi and Tsubaki's lives, guiding their development even before Build Base. As commander, she directed operations against the revived Haniwa threats, leveraging her historical experience and strategic knowledge to coordinate defenses, reconnaissance, and support for the new Jeeg pilot.

Her leadership encompassed tactical command and mentoring younger team members, sharing insights into the original conflict's challenges and sacrifices. The emotional weight of her decades-long separation from Hiroshi Shiba remained a defining aspect of her character, reflecting unresolved personal stakes against the Jama Empire. This arc concluded when Hiroshi reappeared after fifty years, enabling their reunion and participation in the final battle that permanently defeated the Great Jama Kingdom. Their reunion signified closure to her prolonged wait and underscored her enduring connection to the Jeeg legacy.

Physically, she is characterized by gray hair, typically styled with a headband or occasionally a ponytail, reflecting her composed and experienced demeanor as a veteran leader.