Blue Joe, known as Aobei in Japanese, leads the Kooni Trio (called "Scamps" in English). Sent by their father, Great King Enma, to recover a stolen powerful scepter from the protagonist, Blue Joe directs the trio's schemes and confrontations with a tough, authoritative demeanor. This stern exterior, however, masks a notably soft-hearted and sensitive nature, often revealed unexpectedly.

A recurring element involves his romantic feelings for Kammy, a human hairdresser in Moonlight Town. This creates internal conflict, pitting his duties as an oni against his human attachment. Visits to Kammy's salon under various pretenses expose a gentle, flustered side contrasting his usual role. Blue Joe uniquely wields a spoon as his primary weapon during retrieval attempts.

He shares a chromatic theme with his siblings, his blue color symbolizing his position. The trio frequently employs coordinated musical tactics like singing "Shaku Kaese!" (Give us the Scepter!) or the "Kooni Trio no Theme" during operations, though their plans consistently fail due to comedic mishaps. Blue Joe occasionally experiences body-swaps orchestrated by Great King Enma, which never succeed.

Subtle character development emerges through relationships beyond the central conflict. He displays reluctant camaraderie with humans like Tommy, Kazuma's grandfather, who once hosted them. His speech includes the verbal tic "de gonsu." While primarily an antagonist, softer moments—especially concerning Kammy or showing care for his siblings—add dimension, preventing a one-dimensional portrayal. His core traits and objectives remain consistent throughout the series.