Princess Fabia Sheen, a central figure from the planet Neathia, emerges as its princess amidst the conflict chronicled in *Gundalian Invaders*. She first appears disguised as a human, marked by blue hair, green eyes, and a distinctive white-and-orange robe paired with blue boots – an ensemble crafted for blending in on Earth. Her true Neathian form reveals purple-toned skin and large green eyes, a characteristic trait of Neathian royalty.

Driven by the Gundalian invasion of her homeworld, Fabia seeks Earthly allies, recruiting the Battle Brawlers for Neathia's defense. Her resolve is forged in personal tragedy: her fiancé Jin, former captain of the Neathian Castle Knights, was killed by the Gundalian agent Kazarina. Defying her sister, Queen Serena, Fabia rescued Jin's guardian Bakugan, Haos Aranaut, from Gundalian experimentation. This act secured her partnership with Aranaut, though Kazarina's procedures erased the Bakugan's memories of Jin.

Initially consumed by intense hatred and distrust toward all Gundalians, Fabia views them as universally hostile, fueling vengeful actions early in the war. Her combat style showcases considerable physical strength and close-quarters prowess, evident when overpowering opponents like Dan or Zenet Surrow. As a Haos-attribute brawler, her primary Bakugan are Aranaut, Fangoid, Jetro, and Merlix. She later temporarily lends Aquos Centeleon, Subterra Coredem, and Ventus Hawktor to human allies.

Significant development unfolds through key events. Fabia officially joins the Battle Brawlers after exposing Ren Krawler's deception and later becomes a Castle Knight, donning specialized silver-and-yellow combat armor. She gradually overcomes prejudice, accepting Ren after testing his loyalty in battle and allying with the Gundalian turncoat Nurzak. This shift culminates in her acknowledgment that not all Gundalians share Barodius's cruelty, particularly following Kazarina's demise.

After Neathia's victory in the war, her sister Serena steps down, leading to Fabia's ascension as queen in *Mechtanium Surge*. Assuming the throne, she relinquishes Aranaut and its Battle Gear to Castle Knight Captain Elright, symbolically ending her active brawling status. She gains a new guardian Bakugan, Haos Exceed Wavern, paired with the Battle Gear Silver Daybreaker. Fabia also joins Team Grey, continuing her planetary stewardship in this new role.