Tatsuya Yūki, heir to a prestigious lineage burdened by expectations of corporate succession, defied his rigid academic upbringing at age seven when childhood friend Toru ignited his obsession with Gunpla battles. Crafting iconic mobile suits like the crimson-hued ν Gundam Vrabe and RX-93-ν2V Hi-v Gundam Vrabe, he earned the battlefield epithet "The Crimson Comet" through blistering tactical maneuvers. Corporate obligations exiled him to London, where resentment over restricted Gunpla pursuits dissolved upon meeting artisan Takeshi Iori—a encounter that rekindled his belief in creative freedom.

Returning to Japan as Seiho Academy's student council president and modeling club leader, he showcased mastery in both Gunpla craftsmanship and strategic combat. His rivalry with Sei Iori and Reiji crystallized during a test battle wielding the MS-06R-AB Zaku Amazing, where he simultaneously dominated the arena and provoked breakthroughs in the Build Strike Gundam's design.

Cloaked in sunglasses and a trench coat, he operated as PPSE’s shadow agent "Meijin Kawaguchi III," piloting advanced prototypes like the PPMS-1M Kämpfer Amazing while juggling corporate espionage and tournament obligations. This double life culminated during the World Tournament semi-finals against Julian Ayers Mackenzie, where he chose integrity over victory, forfeiting the match to uphold his principles.

Later, at Yajima Stadium’s exhibition battle, he allied with Sei and Nils Nielsen against the Gunpla Mafia, deploying the MSM-07-A Amazing Z'Gok to expose subterranean sabotage tactics—including detecting paint thinner masquerading as groundwater. His relentless ethics and adaptability during crises solidified his legacy as a tactical visionary.

Spanning manga *Gundam Build Fighters Amazing* and *Gundam Build Metaverse* appearances, Tatsuya’s journey traces a metamorphosis from duty-bound heir to mentor and icon—a testament to self-determination forged through the alchemy of plastic models and particle-system warfare.