Fabia Sheen, Princess of Neathia and younger sister to Queen Serena, possesses navy blue hair, green eyes, and distinctive pink earrings. Her human disguise features a white and orange robe with layered elements and blue boots, reminiscent of earlier series attire. Her true Neathian royal form reveals purple skin and large green eyes. As a member of the Castle Knights, she wore form-fitting combat armor accented in silver and yellow; upon ascending to queen, she adopted regal robes like her sister's.

Her story centers on Neathia's invasion by Gundalia. Engaged to Jin, captain of the Castle Knights, she endured his death at the hands of Gundalian agent Kazarina. Jin's guardian Bakugan, Aranaut, was captured and subjected to memory-erasing experiments. Defying Queen Serena's orders, Fabia infiltrated Gundalia to rescue Aranaut, forging a new partnership despite his lost memories. This loss fueled a vendetta against Gundalians, whom she initially perceived as universally hostile. She sent the Phantom Data distress signal to Earth, leading to her arrival in Bakugan Interspace.

Fabia combines fierce loyalty with considerable physical prowess, overpowering opponents like Dan Kuso and Zenet Surrow in close combat. Grief over Jin's death manifested as vengeful hatred toward Gundalians, driving her early actions. This mindset evolved through interactions with former enemies like Ren Krawler and the mercenary Nurzak. Witnessing their betrayal by Emperor Barodius and recognizing shared suffering – such as Kazarina's abandonment of Lumagrowl mirroring her own loss – enabled her to overcome prejudice. A pivotal brawl testing Ren's loyalty led to her accepting his redemption and inducting him into the Castle Knights. Her leadership extended to strategic missions like shield generator reactivation and intelligence operations against Gundalian forces.

Throughout *Gundalian Invaders*, Fabia served as the Haos brawler for the Battle Brawlers. Her guardian Bakugan was Aranaut, supported by Haos Fangoid, Jetro, and Merlix, equipped with Battle Gear like Silver Battle Crusher. Key battles included early victories against Koji Beetle, losses influenced by Ren's sabotage against Jesse Glenn, and collaborative wins with Jake Vallory against Ren and Jesse. Her combat record showed initial struggles but gradual improvement. Significant contributions involved exposing Ren's deception, facilitating the Battle Brawlers' journey to Neathia, orchestrating Bakugan substitutions for human allies, and participating in critical missions like the defense of shield generators. She demonstrated tactical ingenuity during "The Secret Switch," engineering a Bakugan swap between Dan and Shun to outmaneuver Stoica and Jesse.

In *Mechtanium Surge*, Fabia assumed the throne as Queen of Neathia after Serena became an ambassador. She relinquished Aranaut and Silver Battle Crusher to Captain Elright, symbolizing her transition from active brawler to ruler. Elright provided her with a new guardian Bakugan, Haos Exceed Wavern, and the Battle Gear Silver DayBreaker. She later joined forces with Almaz Vontana as part of Team Grey.

Fabia's cultural context reflects Neathia's collectivist society, emphasizing community bonds and shared goals. This underpins her profound identity crisis after Jin's death and her subsequent integration into the Battle Brawlers as a surrogate community. The society's initial isolationism ("Neathian bubble") and distrust of outsiders informed her early reluctance to collaborate with non-Neathians, later overcome through proven alliances. Unique traits include her royal purple skin coloration and parallels to historical figures like Byzantine Empress Fabia Eudokia.