Curse (カース) is Risu's magic user persona which controls most of his well being. It is commanded by surrounding hostility.
Long skeletal mask with four eyes, wears a long black cloak covering most of his body. Chains with sharp edges float around him and he has another pair of hands peeling out of the palms of his hands. Before merging with Risu, it used to have the appearance of a ghostly figure similar to him, engulfed in smoke and fleas, hinting at a relation to decay, pestilence or death.
Uncontrollable fury towards hostiles in his surroundings. Is forced to attack anyone with hostile emotions.
Created when Risu was killed by the Cross-Eyes' Boss, Curse wandered the Magic User Realm in order to find him and curse him to death, coming to every place The Boss used to go and kill every person that tried to attack it until Curse found and pursued him to Hole.
Following him through the magic door created by Dokuga, Curse ripped Kai's head off, devouring it, and invaded his body from his neck. At that moment, the remaining movement in Kai's arm broke a bottle of Ebisu's smoke that Dokuga had given him, mixing the "Entity" influence present in Kai's body, Curse's magic and Ebisu's magic, canceling Curse's effects and trapping it inside of a newly grown head with reptilian features.
Curse remained inside Kaiman for over two years. At some point, Kaiman learnt of Curse's existence within him, and used him as an improvised interrogation method. By biting the head of Magic Users and waiting for Curse to tell them the same phrase over and over again, "You are not the one", because Curse was referring to the fact neither of them was The Cross Eyes' Boss nor Ebisu, the reason why Curse was trapped inside Kaiman's head, to begin with. Asking them what "the man inside his head" had said, Kaiman subsequently slaughtered the Magic Users after not getting a satisfying answer. Curse is the last thing Kaiman saw, through the memories of Kai, standing in the corner of the passage where he later was found by Nikaido. That memory would trigger the constant urge of Kaiman to know who that person was, repeatedly trying to look inside his mouth to see Curse, believing it was, in some form, his former self before his transformation. During its time inside Kaiman it wandered through Kaiman's mind and saw the secret of his pseudo immortality.
It was finally released from Kaiman's body (now Aikawa's body) after Ebisu was killed by her doppelganger doll, canceling her magic and leaving Curse to continue where it left off. But since Aikawa was killed around the same time by En, now without purpose, Curse went straight to the now resurrected Risu, trapped inside the Cross-Eyes Hideout, and merged with him in a similar way to its attempt to kill Kai, entering his body through his mouth. Causing excruciating pain to him, it forced Risu to morph into a reaper-like creature with a skeletal mask and chains growing from his back attached to the stakes of his clothes, as well as a new set of hands grown from his palms.
Curse possessed Risu for over a month, aimlessly patrolling the Magic Users Realm and killing anybody who had killing intents towards them, until he sensed the resurrected Cross-Eyes' Boss, flying straight to him until, once more, it was about to kill him when it was interrupted by Haru's song, as the only thing capable of destroying a Curse-type magic is the song of a Devil. Curse calmed down, leaving the control of the body to Risu, and only activating itself on sensing killing intents towards Risu, until the latter was able to control Curse at will.
Risu (transformed into Curse) is present in the battle inside The Central Department Store, showing how powerful Curse's magic actually is by redirecting a direct slash of the Store's Kitchen Knife against the now Devil-ascended Kai.
After Risu fulfilled Ai/kawa's dying wish, slicing his head with the Kitchen Knife to ensure Hole's death, Curse was finally dispelled, showing how it vanished in the air and leaving Risu to fall to the ground. This made Risu really desperate and angry, knowing that once again, he was a useless person unable to produce magic, though this made Kawajiri laugh, who made fun of him for it.