Fudōmyō Ō, also known as Acalanātha, stands as a wrathful Wisdom King. His role is that of a protector deity, battling earthly vices and confronting Mara, the demonic force threatening balance and corrupting humanity. He operates alongside other enlightened beings, including the Thirteen Buddhas, in their collective mission to shield the world from these corrupting influences.

His characterization centers on a fierce, volatile nature manifesting as intense anger. This quickness to rage presents a recurring personal challenge, reflecting internal struggles inherent to his divine duties. He shares a deeply contentious history with Dainichi Nyorai (Vairocana), resulting in persistent conflict and mutual animosity. Their relationship is defined by frequent arguments and unresolved tension rooted in past disagreements.

Across the narrative, this antagonistic dynamic evolves. Critical confrontations against shared threats force Fudōmyō Ō and Dainichi Nyorai into collaboration. Through these joint efforts, they gradually reconcile, acknowledging their respective flaws—including Fudōmyō Ō's struggle with anger—and move towards mutual respect and renewed cooperation. This resolution culminates in their combined action overcoming a major crisis, solidifying their restored alliance.

While fulfilling his protective duties, Fudōmyō Ō remains vigilant against manifestations of human vice. His actions contribute directly to the conflict against Mara, positioning him as a formidable force aligned with the enlightened beings' goals. His presence underscores themes of overcoming internal discord to achieve unity against external corruption.