Curse Devil

The Curse Devil (呪いの悪魔) is a devil that embodies the fear of curses.

Appearance
When summoned, the Curse Devil manifests as a large, two-headed skeleton with horns, its right skull apears human while the left skull has three eye slits and longer teeth. The Curse Devil has clawed hands and a large distended ribcage.

Whenever it speaks to someone the Curse Devil appears as a dark pair of lips hovering in darkness or as a monstrously large mouth.

Personality
The Curse Devil's personality is currently unknown.

Eternity Devil arc
Aki considers using the Curse Devil's sword to defeat the Eternity Devil but Himeno restrains him with the Ghost Devil's arm.

Katana Man arc
During his battle against the Katana Man, Aki pulled out his Curse Spike to pierce Katana Man's body three times. This trigger served to summon the Curse Devil on Aki's behalf who manifested behind the Katana Man and picked him up before biting him and killing him.

Aki later asks the Curse Devil how much life span he has left after using the Curse Devil's power, and the Curse Devil states that he has two years remaining.

International Assassins arc
Tolka's master uses a nail to stab Denji three times without him noticing. She explains her contract with the Curse Devil to her apprentice and entrusts the fourth and final stab for him to perform as a test. If he succeeds then she will reveal her other devil contracts to him.

Tolka lays a trap and manages to stab Denji by having him step on the nail. The Curse Devil appears and picks up Denji, violently biting into him and killing him.

Abilities
Curse: Upon it's contractor stabbing their target a few times with its nail, the Curse Devil will manifest itself, pick up the target by their arms in a cross position, and mortally wound them by biting into their shoulders and necks while crushing their arms.

Contract Creation: As a devil, the Curse Devil can bestow contracts upon humans for a price. The contracts with it seen so far are:
 * A contract with Aki Hayakawa. In exchange for some of his lifespan, Aki can use the Curse Devil's power, Aki's contract requires the nail to be stabbed 3 times.
 * A contract with Santa Claus. In exchange for the loss of sensations on several of her fingers, Santa Claus can use the Curse Devil's power, its contract requires the nail to be stabbed 4 times.

Blood Consumption: As a devil, the Curse Devil should be able to restore its health by consuming blood.

Revival: As a devil, the Curse Devil should revive in Hell after being killed effectively making it immortal.

Trivia

 * Curse devil's use of rituals involving nails is likely a reference to Ushi-no-Toki-Mairi, a Japanese cursing ritual involving the insertion of a nail into a sacred tree or effigy.