Maou is the current leader of Hell who had acquired the position when Mavuro left upon conceiving Guri.
Feeling that he wasn't fit to rule over Hell, Maou tried to convince Mavuro to reconsider; when that didn't work in his favor, Maou set his eyes on Guri as a potential heir. Maou first appears in episode six of the anime, in which he makes himself an univited guest at Kami's residence. Apparently, Maou and Kami tend to have beverages together a few times, but they also argue on which direction Guri should take. Seiji bluntly tells the two that Guri isn't the type to be interested in either responsibility, which they acknowledge. Both deities agree to stand aside on what should be done for Guri.
Maou reappears again having manipulated a young man into dating Guri. He would have succeeded at the last moment had Guri not have been reminded of a special moment between her and Seiji. Having failed, Maou removes his influence from the young man, and gets confronted by Korari for interfering. At some point, Maou makes acquaintances with Shikimi, and makes a deal with her. As part of the plan, Shikimi manipulates Guri into avoiding Seiji for an entire week, claiming it's to help her realize her feelings for Seiji. When Guri is found, Seiji bluntly tells her that she had been a thorn in his side since they first met. This causes Guri to retreat into black feathers. Maou arrives to gloat about how Guri had fallen because of Seiji neglecting her for a week. Guri erupts from the feathers as a demon, and goes out to reap the love from the populace. Before leaving, Maou is reminded of a promise that he had made to Shikimi, of which the implications are unknown.
Despite succeeding at transforming Guri into a demon, Maou realizes in the final episode that even then, she would still show no interest in becoming the new Maou. Maou thinks back to the time in which Mavuro left Hell upon becoming engaged to Kami. Even though she insisted that he would make a great successor, Maou found himself becoming pressured by this great responsibility with which he prohibited most of the demons from acting on their malevolent nature. Sometime later, Maou is informed that Mavuro separated from Kami, after he had cheated on her. Angered, Maou fights with Kami over his behavior; it is there that he met a young Guri who was asking her father for money so that she could buy some manga books. Since then, he felt that Guri was the rightful successor of the Maou legacy.
After Guri returns to her angelic form and escapes Hell with Seiji and the others, Maou's whereabouts are unknown. Whether he intends on getting Guri back or not is also disclosed.
Maou is a fair-skinned, slender man that appears to be in his early to mid-30s. He has purple hair with his left bang coming down to his chin. He wears golden rimmed glasses and his eyes have black sclera and orange irises. He is normally seen wearing a white suit with a light pink button-down shirt. He also wears black dress shoes, dark red gloves, and a white hat with a light pink stripe.
Despite being a demon and the ruler of Hell, Maou is surprisingly honorable (for a demon) and doesn't seem to actually be evil. On the contrary, it is shown that since becoming the ruler of Hell, Maou has prohibited the demons from acting on their generally malevolent nature and attacking humans. This suggests that Maou may have compassion for humans. Although he made a deal with Shikimi, he was reluctant in fulfilling his end of deal by transforming her into a demon. He expressed disgust at Shikimi's twisted personality, saying that she "already is like a demon," suggesting that he has a low opinion of his own race.
Maou has a low level of self-confidence as he believed that he was not fit to rule Hell. When his love interest, Mavuro, turned him in down in favor of Kamisama, he continued to love her and became enraged when he discovered that Kamisama cheated on her. As he saw much of Mavuro in her daughter, Guri, he has sought to transform her into a full demon so she may succeed him as leader of Hell.
He seemed saddened when Guri expressed no interest in succeeding him, but also appeared nonchalant as she was brought back to the light; suggesting that he doesn't want to force Guri to do anything she doesn't want. Whether or not he still wishes for her to succeed him or not is unknown.