As one of Phalanx's foremost generals, the demon Arma was tasked not only with hindering Firebrand's quest to reacquire the six crests of power, but was also personally entrusted with the protection of several of these crests. Though he is a recurring thorn in the protagonist's side over the course of Demon's Crest, sparring with him on three separate occasions, he displays a much greater amount of respect for Firebrand's abilities than his master Phalanx exhibits, even going as far as to compliment his adversary's prowess after their first encounter. This deference eventually grows into the realization that he is not up to the task of defeating the red demon, as he fatalistically acknowledges before their ultimate confrontation that it is his last chance to overcome Firebrand. After being defeated once more, Arma chooses as his final act to imbue his life essence within the Crest of Time, thereby granting Firebrand his own power in open defiance of his master.
Each of the player's three battles with Arma are essentially similar, though a single new attack is added to his regular patterns each time. When first he appears, he attacks alternately either by diving at the player or firing a single projectile in their direction. On second encounter, he also uses a whirlwind attack which gradually draws players toward its epicenter. His final form also uses a stronger projectile attack when threatened. Defeating his first, second, and third forms rewards the player with the Crests of Earth, Wind, and Time, respectively. It is possible to complete the game without fighting all three forms, however this results in a "bad" ending in which the demon realm is thrown into chaos.