Jack Joe

Jack Joe is friendly, affectionate and considerably gentler than his appearance suggests. He is comfortable around humans and quickly accepts Kiyoshi despite the latter being an exorcist, contradicting Kiyoshi's childhood assumption that demons are inherently malicious.

His strongest attachment is to Nehan, with whom he has spent much of his life. Their friendship is based on genuine companionship rather than merely the supernatural contract connecting them.

Jack Joe's demeanor changes drastically when his demonic power overwhelms his usual personality. In that condition he becomes ferocious and difficult to control, with Nehan serving as the person most capable of reaching him.

Jack Joe possesses extraordinary physical strength, speed and regeneration. His more powerful fighting state can surprise even an accomplished exorcist such as Tsurugi Hijiri, and his blows have enough force to send powerful opponents flying. He can rapidly regenerate serious wounds, including injuries inflicted by exorcist weapons.

As Nehan's contracted demon, Jack Joe can combine his abilities with his partner. Their contract allows Jack Joe to enter Nehan's shadow and merge his power with him, producing a combat form capable of generating multiple elongated arms and greatly increasing their offensive capabilities.

Jack Joe's apparently simple background conceals his former position as a Demon Lord. His uncontrolled fighting state is connected to the enormous power he possessed before losing his memories in the human world.

Jack Joe enters the story when Kiyoshi begins attending Naraku Municipal High School and tries to make friends. Kiyoshi soon learns that the frightening-looking creature accompanying Nehan is a demon, forcing him to confront the difference between the monsters that destroyed his childhood and demons capable of living peacefully with humans.

His presence attracts the attention of the Knights of Light. Tsurugi and Sousuke Hitsugi pursue him as a dangerous demon, placing Kiyoshi between the exorcist organization and his new friends. Kiyoshi's decision to protect Jack Joe becomes an early demonstration that he judges demons by their actions rather than their species.

During the Black Parade, Jack Joe's forgotten past becomes central to his confrontation with Bakku Yoraku, an old friend and rival from his life in the Demon Realm. Jack Joe is revealed to have once occupied the position associated with the Fifth Demon Lord before his disappearance and memory loss.

Nehan Sanzugawa is Jack Joe's childhood friend, contracted partner and closest companion. Nehan found him after he arrived in the human world without his memories, and the two subsequently grew up together.

Kiyoshi Harai befriends Jack Joe after entering high school and chooses to protect him when exorcists target him.

Tsurugi Hijiri initially regards Jack Joe as a demon that must be exorcised and fights him during the conflict surrounding Nehan.

Sousuke Hitsugi accompanies Tsurugi during the operation against Jack Joe, but later contributes indirectly to the effort to heal him after he is critically injured.

Bakku Yoraku was Jack Joe's friend and rival in the Demon Realm, and their reunion during the Black Parade forces Jack Joe to confront the life he had forgotten.