Mariyus Casteledo is the alias assumed by Princess Marielle D'Hontensia after the brutal rebellion led by Duke Rugis Camellia. During the siege of Hortensia, her father, the king, was slain by Rugis following his werewolf transformation. Knight Templar Maurice Baudelaire rescued her, advising she cut her hair and take a new identity to evade the Pope and other enemies targeting the royal family. Maurice adopted Marielle, relocating to the Albert Dominion where she lived under his protection. Her appearance features green eyes and long blond hair usually tied back. She wears a hooded blue-and-white jacket with gold trim over metal chainmail, black pants, and thigh-high brown boots. A rapier is carried on her left side. Initially serving as a servant and apprentice knight to Alfred Albert, Mariyus trained alongside him under Maurice's guidance. She concealed her true identity, fearing recognition and capture by forces loyal to the Pope. Despite this caution, she participated in missions, including investigations into a petrification plague linked to the church. During one mission, suspicions about her identity led to her capture by Didier Viardot, a high-ranking ecclesiastical knight. After her identity as Princess Marielle was revealed, her demeanor shifted from cautious reserve to increased assertiveness. She openly acknowledged her royal status, leveraging her position to oppose the Pope's machinations. Her role expanded beyond Alfred's squire as she engaged directly in the conflict against church corruption. A pivotal moment occurred during the final confrontation with Pope Vall d'Hebron, who sought ancient Magonian power to solidify control over Hortensia. After Vall's defeat and Rugis's subsequent attack, Marielle demonstrated a latent ability tied to her royal lineage by reviving the mortally wounded Alfred. This act resulted in Alfred acquiring a demonic eye. Following these events, she reclaimed her position as heir to the throne and delivered a public address affirming her leadership, with Alfred at her side.