Didier Vialdo, the "First Black Knight," is a formidable Temple Knight clad in imposing black armor accented with gold lining, a matching cape, and helmet. He wields both a rapier and an axe as his primary weapons. Recognized as the strongest warrior within the Order of the Church of the Orthodox Church of Hortensia, his combat prowess surpasses even renowned knights like Fernando Ober and Leon D. Olivier. Hailing from the United Kingdom, he operates under the Church's authority. Following a rebellion that destabilized the kingdom, Vialdo aligns with Pope Alexis Vall d'Hebron to consolidate power. He enforces the Church's influence by leveraging the young puppet ruler, King Charlot D'Hortensia, installed after the uprising. His actions focus on suppressing dissent and extending ecclesiastical control over regions such as the Olivier Dominion and the Albert territory. Vialdo possesses significant expertise in magic and alchemy, employing spells and potions to achieve tactical objectives. A key artifact under his command is the "Black Book," a Magonian Relic enabling manipulation of "Oaths"—sacred contracts binding Hortensia's populace. He commands a loyal army of knights and mercenaries, demonstrating strategic acumen in orchestrating military campaigns and political schemes. His combat capabilities are further augmented by the Noble Phantasm "Royal Omnislash: Black Knight of Justice," a devastating multi-slash technique executed simultaneously with sword and axe to instantly eliminate adversaries. His interactions are defined by conflict, opposing protagonists Alfred Albert and Adelheid Olivier, whose resistance to Church authority he perceives as a threat to stability. Key adversaries include Rugis F. Camellia, the instigator of the rebellion that plunged Hortensia into chaos. Despite his antagonistic role, Vialdo maintains a strict adherence to his personal interpretation of justice and order, viewing his methods as essential for the kingdom's protection.