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
As a Devil, the Curse Devil possesses all of the standard devil abilities. As a contract devil, it showed its abilities based on its contracts.

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. The contracts with it seen so far are:
 * In exchange for some of his lifespan, Aki Hayakawa can curse his targets by stabbing them with his nail-shaped sword 3 times. Each time he stabs his target, he shouts Fire! and a finger of the Curse Devil manifests to flick the nail.
 * In exchange for the loss of sensations on several of her fingers, Santa Claus can curse her targets by stabbing them with a nail 4 times.

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.