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Cursed seals are cursed black-magical markings to seal power given by evil beings. They can either transform someone, make someone's brains turn to jelly whenever the applicant of the seal wills it, or can be used to compact with (a) demon(s) on one of someone's hands to execute "Demon Wave" techniques.

Other seals seal demons in people's bodies, giving them a tremendous amount of power from the demon.