Isuzu Fujiwara is the full-time physician at the Giou family's infirmary within Twilight Mansion. His primary duty is providing medical care to the residents and members of the Giou Clan. He obsesses over researching the Duras, the demonic adversaries of the Giou Clan. This research frequently consumes him entirely, leading him to neglect showering, shaving, eating, drinking, and sleeping. These intense, sleepless periods often culminate in physical collapse, causing him to pass out for days amid scattered books and papers. His appearance shifts dramatically based on his research immersion. When deeply engrossed, he appears disheveled, ghastly, and intimidating. After grooming himself—shaving and cleaning up—he transforms into a young-looking, handsome man with mid-length, dark blue wavy hair. His interactions and treatment methods frequently manifest as perverted, regardless of intent. He harbors a specific, intense fascination with the Duras, particularly fixating on examining Luka Crosszeria, a Duras defector aligned with the Giou Clan. This fixation drives him to repeatedly express his desire to examine Luka. Despite Luka's typically stoic and protective nature, especially concerning Yuki Giou, Isuzu uniquely provokes significant anger and irritation in Luka without threatening Yuki or causing physical harm. His presence focuses exclusively on his role as clan doctor and interactions driven by his obsessive research.