Julius Euclius originated as Julius Juukulius, son of runaway noble Klein Juukulius and a commoner. Orphaned by a flash flood, he was adopted by his uncle Alviero Juukulius, head of House Juukulius, gaining noble status. Within this house, he became the adoptive older brother to Alviero's frail, sickly biological son, Joshua Juukulius. Julius consistently supported Joshua, transforming the boy's initial jealousy into deep admiration. As a knight, Julius earned the title "Greatest of Knights" through exceptional swordsmanship and mastery of spirit arts. He formed contracts with six quasi-spirits—Kua, Alo, Ingi, Jiko, Nem, and Neun—augmenting his combat abilities and enabling him to wield multi-colored mana for offense and defense. His noble bearing and composed demeanor solidified his reputation as a paragon of knightly virtue. Julius served the Anastasia Camp as a key supporter of merchant candidate Anastasia Hoshin during Lugunica's Royal Selection, influencing Joshua to join the same camp. He initially clashed with Natsuki Subaru over perceived disrespect toward knighthood, culminating in a duel where Julius stripped Subaru of his mana—a punishment straining their relationship. Mutual respect developed as Subaru matured, notably during their cooperation against the Witch's Cult in Arc 5. Julius maintained a professional rivalry with Reinhard van Astrea, their interactions marked by mutual acknowledgment. His development showed growing flexibility toward non-traditional approaches, accepting Subaru's unorthodox strategies despite initial reservations. He evolved his perspectives on nobility and duty, mentoring Joshua to overcome prejudice against demi-humans, reflecting his commitment to justice beyond rigid hierarchies. Following Joshua's incapacitation by the Sin Archbishop of Gluttony, Julius's resolve to protect others intensified, shaping his actions in subsequent conflicts. In non-canonical appearances like the crossover *Isekai Quartet*, Julius interacted with characters from other worlds in a school setting. These portrayals do not contribute to his official character development or backstory. No concrete information exists regarding his role in OVAs, movies, or other spin-offs outside the main series.