Aobee leads the Kooni Trio, three young oni siblings dispatched by their adoptive father, Great King Enma, to retrieve a stolen scepter from the protagonist. Though only seven years old and putting on a tough front as leader, he harbors a soft-hearted and gentle nature. He hails from Enma World, where the trio exchanged their battle sticks for giant cutlery as makeshift weapons; Aobee wields a knife.

His traditional background is reflected in his speech patterns, using the archaic pronoun "Washi" for himself and ending sentences with "de gonsu." Aobee develops a recurring affection for Komachi, a human classmate of Kazuma. This contrasts with his oni role, and he remains unaware that another oni, Green Oni, has feelings for him, showing occasional obliviousness to social cues.

Aobee persistently collaborates with his siblings, Akane and Kisuke, in repeated but unsuccessful attempts to reclaim the scepter. Their plans typically involve disguises or comedic schemes that fail due to the protagonist's cleverness or unforeseen circumstances. Despite being antagonists, their efforts are lighthearted, emphasizing their unity and shared purpose over malice. The trio sometimes breaks into musical themes like "Kooni Trio no Theme" and "Shaku Kaese!" during their missions.

His character design features blue coloration, matching the trio's chromatic theme (red for Akane, yellow for Kisuke), leading to the localized name "Blue-Joe" in international adaptations. While focused on the scepter quest, later episodes and specials, such as the Heian-era conflict in "Heian-chō Onigami Kessen," reinforce his ongoing commitment to this mission alongside his siblings. No significant long-term development or resolution to his quest is documented, maintaining his role as a persistent yet non-threatening adversary driven by familial duty.