Vixur Ul Shasta commanded the Order of Dark Knights and sat on the Council of Ten Lords, governing the Dark Territory of Underworld under the "Law of Power" where strength dictated authority. A pragmatist with a sense of honor rare among his conquest-driven people, Shasta foresaw catastrophic casualties and internal tribal strife from war with the Human Empire. He secretly pursued peace.

His perspective was forged early. Born to a novice knight, he entered a Dark Knights cadet school as soon as he could wield a sword. Exceptional skill drew the attention of the previous Commander, who took him as an apprentice. Around twenty, after his mentor lost an arm to the Human Empire's Integrity Knight Bercouli Synthesis One, Shasta was ordered to kill his master in a duel to inherit the elder's knowledge of "Incarnation" – the power of will manifesting physically. This act scarred him permanently with guilt. At thirty-seven, during another clash with Bercouli, Shasta demonstrated Incarnation powerful enough to deflect a Divine Object-class weapon. Bercouli noted his will stemmed from gratitude to predecessors and hope for successors, not hatred, cementing Shasta's commitment to peace.

Learning of Administrator Quinella's death, Shasta saw an opening for diplomacy. He confided his plan to his subordinate and romantic partner, Lipia Zancale: assassinate four key pro-war lords, including the Goblin chiefs and Dark Mage leader D.I.L., to stabilize the Dark Territory. Immediately after revealing this, he proposed marriage to Lipia.

Their efforts shattered with the arrival of Gabriel Miller, logged in as the super-account "Emperor Vecta". Gabriel effortlessly killed Shasta's rival, Vixur, forcing the tribes to pledge loyalty under the "Rule of the Strongest". Two days later, Lipia attempted to assassinate Vecta and was executed. When Vecta displayed her severed head, Shasta drew his Divine Object-class sword, Oborogasumi – a blade transforming into mist-inflicting slashes – and unconsciously activated its Armament Full Control Art. Before he could strike, the Assassin's Guild leader Fu Za poisoned him with a lethal needle.

In his final moments, Shasta's Incarnation unleashed Oborogasumi's recollection release, creating a tornado of destructive willpower that physically manifested his form to strike Vecta's consciousness. Gabriel Miller's corrupted Fluctlight absorbed and vaporized Shasta's will, nullifying the assault.

Shasta's legacy endured. His analysis cited the Dark Territory's environmental hardship – poor soil, scarce resources, and lack of protection – as the root cause of its aggression. After the war, the Human Empire sent supply convoys and facilitated land expansion beyond the End Mountains, actions validating his belief that stability could avert conflict.