Katsuto Jūmonji is a senior student at First High School and heir apparent to the Jūmonji family, one of Japan's ruling Ten Master Clans governing magical society. He forms part of the influential "Big Three" alongside Mayumi Saegusa and Mari Watanabe, recognized for his formidable magical abilities and leadership. Standing 186 cm tall and weighing 90 kg with dark brown hair and brown eyes, his imposing physique commands attention. His magical expertise lies in "Phalanx," a Multiple Move-Type Defense Magic that weaves layered barriers capable of shielding allies and crushing opponents offensively, reflecting his role as protector and enforcer. Representing the Jūmonji family's interests at the Master Clans Conference, he participates in decisions affecting Japan's magical community. The Jūmonji hold significant influence in the Kantō and Izu regions, monitoring magical activities to maintain stability. Katsuto embodies the family doctrine of strength and responsibility, intervening to protect the Ten Master Clans' reputation, such as demonstrating his prowess in a Monolith Code match after Tatsuya Shiba defeated Ichijō Masaki. His composed demeanor and strategic mindset emerge during crises. He assisted in repelling USNA STARS operatives attacking a research facility during the Watatsumi Series incident. Later, during the Ten Master Clans' telegraphic meeting on the Watatsumi girls' custody, he supported the Yotsuba family's claim due to their capability. Across all media, including the spin-off *The Honor Student at Magic High School*, he consistently acts as a stalwart guardian of tradition and order, leveraging his authority within the school and the Ten Master Clans to counter threats to Japan's magical equilibrium.