Obi is a 21-year-old male with black hair and brown eyes, though some sources describe his hair and eye color as olive. Initially an assassin serving advisor Haruka, his mission was to frighten Shirayuki away from the royal court to remove her as an obstacle for Prince Zen. When this mission failed, Obi entered Prince Zen's service.

His duties evolved from delivering messages and surveillance to primarily protecting and minding Shirayuki. Despite a confrontational first encounter where he shot an arrow near Shirayuki to intimidate her, they gradually formed a close friendship and spent significant time together. Obi harbors growing romantic feelings for Shirayuki, addressing her politely as "Miss," and accompanies her alongside Ryuu during meetings with Zen. His presence at these outings carries an undercurrent of tension, perceived as an actual threat compared to Ryuu; his lighthearted jokes mask a more dangerous complexity.

Obi maintains an enigmatic and mysterious demeanor, often wearing a mask that enhances his intimidating reputation, with initially unclear motives for joining Zen. Beneath this exterior lies a friendly, caring, and protective nature. He adeptly shifts between a charming, approachable persona and the alert, dangerous instincts honed as an assassin, making him exceptionally suited for protection. Over time, he also formed friendships with Mitsuhide and Kiki. Physically, he bears a scar and possesses notably exotic eyes.