Diabal is a horned individual who dwells deep within Caislean Merlin. Blind, with white eyes, he has long brown hair and small horns. His body bears bandaged wounds from severe torture, including mutilated fingers: two fingers cut halfway on his left hand and the middle finger half-cut on his right.

Consuming paranoia and deep wariness define him now, a stark shift from his naive youth. This stems from a traumatic betrayal that led to his capture and torture by the Inquisition. After escaping, he lives hidden, avoiding all contact and maintaining constant vigilance.

His key relationship is with Piodon, who initially rescued him from the Inquisition, raised him, and trained him in Fantasia manipulation. Piodon later betrayed Diabal, delivering him to the Inquisition when Diabal asked too many questions. This betrayal caused Diabal's torture and escape, cementing his permanent distrust and isolation.

As an infected, Diabal resists Nemesis presence. He wields Fantasia with his bare hands, a trait shared only with other horned infected like Seth and Piodon. His primary ability summons "Spectrums" – lifelike giant projections of objects from his magic device. He uses these to deceive Magic Knights into perceiving them as real Nemesis threats.

A specialized transformation, marked by spreading black, gangrene-like patterns across his body, grants him massively amplified strength and the capacity to generate violent waves of Fantasia. Diabal also unknowingly accesses shamanic vision, perceiving his surroundings by sensing Fantasia pulsations despite his blindness. He remains unaware of this ability's full potential or his capacity to enter the shamanic plane at will.

Visual depictions in official media include younger portrayals, such as on the back cover of Volume 8, showing him during his initial time with Piodon before betrayal and torture.