Headmaster Osmond, often referred to as Old Osmond, is the aged and wise director of the Tristain Academy of Magic. His background is marked by a significant encounter thirty years prior to the main events of the series, when he was saved from a dragon by a mysterious, injured man from another world, later implied to be an American soldier. This man carried a weapon that Osmond would name the Staff of Destruction, one of which was buried with the soldier and another presented to the royal court.

In terms of personality, Osmond is generally portrayed as a benevolent and grandfatherly figure, yet with a notable tendency toward lecherous behavior. He frequently makes flirtatious remarks or attempts to use his position to get closer to female students and staff, much to the chagrin of those around him. This playful and mischievous side does not diminish his underlying wisdom and competence as the head of the academy. His motivations primarily center on the well-being of the school and its students, but he also has a deep-seated curiosity about artifacts from Saito's world, often examining them to learn more about the place where his savior came from.

In the story, Osmond serves as the head of the magical institution where the protagonist, Louise de la Vallière, studies. His role is often that of an authority figure who provides guidance, assigns tasks, or offers a place of refuge during political turmoil. He is notably protective of the Staff of Destruction, which he keeps hidden. His key relationships include that with his former secretary, Longueville, who was revealed to be an antagonist, and his current familiar spirit, a mouse named Motsognir. He holds a trusting relationship with Saito Hiraga, often asking for his help in identifying and understanding various items that arrive from Saito's home world, as seen when he requested Saito's confirmation on the contents of a secret chest filled with Earth artifacts.

While Osmond does not undergo a dramatic personal transformation in the Rondo of Princesses season, his development is consistent with prior seasons: he remains a steady, if eccentric, pillar of support for the main cast. His abilities as a mage are formidable; he possesses a square-class affinity for wind magic, which represents the highest level of magical skill in the series’ system. Despite his power, he rarely engages in direct combat, preferring the role of an administrator and strategist. His familiar, Motsognir, is often seen on his shoulder or lap, assisting him in small tasks.