Tsubaki Tamashiro is a 17-year-old high school student sharing classes with Kenji Kusanagi and Kyo Misumi. She resides with her grandmother, Miwa Tamashiro—formerly known as Miwa Uzuki, the original Big Shooter pilot 50 years prior—at a shrine where Tsubaki serves as a shrine maiden. This lineage binds her to Build Base's legacy.

She works part-time at Build Base, defending against the Haniwa Empire as co-pilot of the Big Shooter alongside Kyo. Her combat role demands precise coordination to deploy Jeeg's components during missions against Haniwa Phantom Gods, providing critical support to the main protagonist.

Tsubaki shares a complex childhood friendship with Kenji, marked by frequent teasing and outward frustration that often escalates to physical aggression. Beneath this tsundere demeanor lies genuine concern and unwavering loyalty, revealing underlying mutual affection obscured by her irritable or violent reactions.

Her commitment to Build Base stems from her grandmother's pivotal role in the historic conflict against Queen Himika, making the fight deeply personal. Juggling shrine duties, academics, and combat operations, she demonstrates adaptability while navigating battlefield stresses and team tensions. Her development focuses on sustaining emotional resilience amid these dual pressures.