Bel Peol is a prominent antagonist in the narrative, known as a Crimson Lord and a key member of the Crimson Denizen organization Bal Masqué. She holds the title of Arbiter of Reverse Reasoning, also translated as Judge of Paradoxes, and serves as one of the three leaders of the Trinity, originally acting as the Strategist before later assuming the role of Chief of Staff. Her character is defined by a sharp strategic mind, a calculating demeanor, and an unwavering dedication to the cause of her master.

In physical appearance, Bel Peol takes the form of a tall, elegant woman with long, straight light purple or brown hair depending on the adaptation, typically clad in a grey or black dress with fur trim. Her most distinctive feature is her three golden eyes, one of which is located on her forehead. Her right eye is usually covered by a black eyepatch with a red rim and three red circles, a result of an injury sustained during an ancient war. She often wears long gloves, jewelry such as bracelets and earrings, and high-heel or flat shoes, with her design having notable differences between the light novels and the anime.

Personality wise, Bel Peol is a master strategist who is cold, calculating, and deeply committed to the objectives of Bal Masqué. She has no qualms about manipulating subordinates or sending them on dangerous missions if it serves the greater plan, yet she possesses a gift for engendering fierce loyalty in her followers. Despite her ruthless efficiency, she shows occasional signs of care for her colleagues, such as attempting to save a defeated ally. In rare moments, her composure cracks, particularly around the Mystes Yuji Sakai, or more precisely the god inhabiting his body, the Snake of the Festival, hinting at a devotion that borders on personal affection.

Her role in the story is central to the operations of Bal Masqué. Rather than engaging directly in combat, she primarily orchestrates battle plans and strategic maneuvers from behind the scenes, though she is a capable fighter when necessary. She oversees the creation of the Great Binding Chain and is instrumental in the plans to create a new world for Denizens. As part of the Trinity, she works alongside the other two leaders, Hecate and Sydonay, to guide the organization towards its goals. She is often seen interacting with Sydonay, whom she occasionally teases about his feelings for Hecate, and she maintains a deep loyalty to the Snake of the Festival, whose revival she actively supports.

Throughout the narrative, Bel Peol demonstrates notable development in her position and personal history. She lost her right eye during the ancient war that led to the sealing of the Snake of the Festival, and she discards her eyepatch after her master is fully revived. She evolves from a distant strategist to a more directly involved commander, ultimately acting as a loyal subordinate and protector of the Snake of the Festival. She also demonstrates adaptability, as evidenced by her change in title from Strategist to Chief of Staff, reflecting a shift in her organizational role.

Bel Peol possesses several notable abilities that complement her strategic genius. Her personal Treasure Tool is named Tartaros, which grants her the power to bind enemies, cut off cause and effect to nullify an opponent's abilities, teleport Denizens, and create powerful barriers. She also wields a Treasure Tool called the Gordian Knot. In direct combat, she employs a specific fighting style where she aims her first attack at the opponent's face, and when they are distracted, follows with a decisive strike to the upper abdomen. She demonstrated the effectiveness of this tactic in a confrontation with the Flame Haze Wilhelmina Carmel, whom she defeated and humiliated. Her flames are a distinctive gold color, marking her as a Crimson Lord of significant power.