Maō is a malevolent supernatural entity who serves as the primary antagonist of the story. He dwells in a place known as Hell Valley, a cursed location where he encounters the young woman Tamamo after she becomes lost during a violent storm. From that moment, he places a curse upon her that binds her will to his, making it impossible for her to disobey his commands. His background is rooted in the dark folklore of the setting, functioning as a demon of considerable age and evil intent who seeks to spread chaos and destruction across the human world.

In terms of personality, Maō is ruthless, commanding, and devoid of empathy. He exercises absolute control over those he curses and shows no concern for the suffering he causes. His motivations are centered on domination and the fulfillment of his grand ambitions. He commands Tamamo to carry out a series of destructive acts, including ordering her to melt down all the Buddhist statues in Japan to create a giant golden statue, a task that reflects his desire to corrupt and reshape the world according to his own dark design. He does not act out of personal vendetta but rather out of a fundamental drive to impose his will and bring ruin.

His role in the story is that of the hidden puppet master. He does not appear in the foreground for much of the narrative but instead works through Tamamo, whose actions are dictated by his curse. He is the source of the disasters that befall the capital, including great fires and droughts, as he uses Tamamo as an instrument to destabilize society. He also serves as the ultimate obstacle for the protagonist Tobimaru, who seeks to free Tamamo from his influence and defeat the demon king once and for all.

Maō's key relationship is with Tamamo, whom he controls completely through his curse. Their dynamic is one of master and servant, with Tamamo torn between her own emotions and her forced obedience to him. She is unable to resist his commands even when they go against her own wishes, particularly her desire to return to a peaceful life with Tobimaru. Maō also has an间接 relationship with Tobimaru, as Tobimaru becomes his direct adversary, seeking the enchanted halberd carved with a statue of Fudo Myoo, which is the only weapon capable of defeating him.

In terms of development, Maō remains largely static as a character. He does not undergo change or redemption, instead persisting as a force of pure evil until the final confrontation. His defeat comes when Tobimaru hurls the blessed halberd at the giant golden statue that Maō had commanded to be built, piercing its chest and causing it to collapse. However, the battle has a tragic consequence: at the moment of Maō's defeat, Tamamo also vanishes, and because she failed to carry out his final command, she is turned into stone. This outcome underscores the lasting, cruel nature of Maō's influence even beyond his destruction.

Regarding notable abilities, Maō possesses powerful dark magic, most notably the ability to curse individuals and bind their wills to his own. He can also create or command a massive golden golem-like statue, which animates and fights on his behalf. He is associated with fire and storms, and his presence is tied to the supernatural phenomena that plague the land. His power is such that only a specifically consecrated weapon, the halberd imbued with the spirit of Fudo Myoo, is capable of defeating him.