Vixur Ul Shasta commanded the Order of the Dark Knights and sat on the Ten Lords Assembly governing Underworld's Dark Territory. He possessed a towering human stature, short black hair, black eyes, an orderly mustache, and a shallow scar running from his brow to the bridge of his nose. He typically wore plain hemp clothing or full-body pitch-black armor marked with numerous scratches, wielding the legendary sword Oborogasumi.

Shasta prioritized peace and stability, contrasting with other Dark Territory leaders driven by conquest. He feared war with the Human Empire would cause massive casualties, shatter the fragile balance among the Dark Territory's races, and reignite centuries of internal conflict, a perspective shaped by experiences during earlier Dark Territory civil wars. He maintained a romantic relationship with his subordinate Lipia Zancale, openly proposing to her rather than asserting dominance by force—a rarity in their society.

Trained at a Dark Knights cadet school, his combat prowess led to recruitment by the order's commander. Around age twenty, he was ordered to kill his master in combat to inherit knowledge of "incarnation" (willpower manifesting as power), resulting in his facial scar. Years later, battling Integrity Knight Bercouli Synthesis One, Shasta demonstrated sufficient incarnation to impress Bercouli, leading to a non-lethal conclusion and mutual respect. He also fought Integrity Knight Fanatio but left a negative impression after underestimating her upon discovering her gender.

During the Alicization Invasion arc, Shasta saw Pontifex Quinella's death as a peace opportunity. He secretly planned to assassinate rival lords like Dee Eye Ell to negotiate with the Human Empire via Bercouli. Emperor Vecta's (Gabriel Miller) sudden appearance disrupted this plan. Vecta demanded war, gaining other lords' support while Shasta remained opposed. Two days after Lipia Zancale was killed attempting to assassinate Vecta, her severed head was displayed before the Ten Lords. Enraged, Shasta drew Oborogasumi, unconsciously activating its Armament Full Control Art and manifesting a tornado of killing intent. Before he could strike Vecta, Assassin Guild leader Fu Za fatally poisoned him. In his final moments, Shasta's will unleashed the sword's power, creating a storm that damaged multiple tribal leaders and Vecta's consciousness—though Vecta's void-like psyche absorbed the attack. Shasta perished expressing regret over Lipia's death.

His legacy endured through his unyielding desire for peace. His and Lipia's residual wills later reached Kirito, reinforcing the importance of rejecting hatred and continuing to fight for hope despite despair.