Hyōei Isurugi stands as the 26th head of the Isurugi ninja clan, dedicated to upholding its legacy and duties. He appears as a short elderly man with grey hair and a grizzled beard. On missions, he dons an ink-black uniform, a red scarf, and conceals his face with a black fox mask. During peaceful times, he wears traditional dark blue hakama paired with a dark blue dogi.

His personality reveals a profound commitment to his leadership role, marked by strictness in teaching Isurugi-ryu Ninjutsu to his granddaughter, Rikka. Alongside this discipline, he displays a playful nature and deep affection for Rikka, placing her safety above all else.

Regarding relationships, he actively prepares Rikka to become the 28th Master of the Isurugi Ninja. He frequently clashes with his son-in-law, Allen Isurugi, over Rikka's future, though both share unwavering love for her and maintain mutual respect. During a devastating attack on their home by Gradsheim operatives led by Lauren, Hyōei and Allen fight together. They sacrifice their lives to ensure Rikka's escape and protect vital family research data, with Hyōei restrained and mortally wounded by Lauren's esper-controlled daughter. His final act facilitates Rikka's evacuation using animal drones. Posthumously, he appears in a birthday recording for Rikka, revealing a specially designed "Black Fox" cybernetic ninja suit as her gift.

Within the live-action tokusatsu spin-off "BLACKFOX: Age of the Ninja", set in Japan's Edo period, he retains his position as Isurugi clan head. Here, he accepts an assassination contract from Miya, who seeks vengeance against the Negoroshu gang for her father's murder. This decision sparks Rikka's moral opposition to killing. When Rikka challenges his orders, he enforces disciplinary measures, yet his protective instincts remain strong amid escalating conflicts involving the Negoroshu and hidden conspiracies.