Kyoji Mujo is a nineteen-year-old Alter user and the principal antagonist of s-CRY-ed. He originally arrives in the Lost Ground as an agent of the Mainland government, dispatched after the second seismic upheaval to exploit the parallel Alter dimension for economic gain. Almost immediately his ambition outgrows that mission, and he defects to pursue his own vision of absolute power, becoming the de facto ruler of the corrupted local government and an independent renegade driven entirely by greed.

At the core of Mujo's personality is an insatiable hunger that he himself calls a thirst for "the Other Side," the dimension from which all Alter abilities originate. He is calculating, utterly self-superior, and entirely unbound by morality; he views other people's lives as disposable stepping stones toward his goal. His behavior is frequently described as that of a madman, and he displays no loyalty to the Mainland, HOLY, or any person—only to the accumulation of more power.

His central role in the story is that of a hidden orchestrator. While Kazuma and Ryuho clash throughout much of the series, Mujo watches from the shadows, aware that their intense battles can tear open a gateway to the Alter dimension he so desperately seeks. He manipulates events inside HOLY and the Lost Ground to position himself at the center of that dimensional rift when it appears. Later, after absorbing the entity known as Crystal—the same mysterious Alter that attacked Ryuho's family—he becomes even more dangerous, finally achieving the godlike state he craved.

Kyoji Mujo's development follows a steep arc from behind-the-scenes advisor to unrestrained, power-mad tyrant. His delusions of grandeur escalate with every absorbed ability until he reaches a monstrous form, convinced he has at last satisfied his unending thirst. That moment is ultimately his undoing, as Kazuma and Ryuho, separately empowered by the same parallel world, defeat him and Crystal.

Mujo's relationships are defined by exploitation. He treats the twins Elian, whose Alter abilities he later steals, as mere batteries. He absorbs Crystal outright rather than cooperates with it. His connection to Kazuma and Ryuho is indirect but critical: he needs their rivalry to break open the dimensional barrier and sees them as tools. He has no meaningful allies, only pawns.

His Alter ability is fundamentally versatile because he can forcibly absorb the powers of other Alter users and make them his own. His original and signature ability is Absorption, which lets him drain Alter energy through his breath or hands and integrate the target's powers. After absorbing Crystal's energy, he gains the ability to generate powerful electrical fields and fire paralyzing bolts of electricity. His most recognizable combat form is the duo-technique White Trick and Black Joker, also referred to as Black Joker and White Fist. In this form his right arm turns black and his left arm white, allowing him to release massive electric shocks or transform his arms into a high-speed drill. Mujo can also create defensive shields of raw Alter energy, open portals to travel into and out of the Alter dimension, summon the Alter Crystal to fight alongside him, and, after stealing the abilities of the Elian twin clones, channel Alter power into technological systems to reactivate whole fortresses. In every engagement he relies on sheer accumulated force, making him one of the most overwhelmingly powerful Alters in the series until only the combined efforts of his two greatest rivals can finally stop him.