Мао

Maou the Great Stygian of Abe (Temp) is a demon and last boss of the game that Nagi is playing in episode 10. She wears a talking skull named Gaikotsu on her head who punishes her when she tries to help the good guys. Maō is chained to her chair and resides in her fortress on top of a tower. She tries to capture a hero from the outside world using her guillotine fishing rod to play the game and send her to the underworld. Maō ends her sentences with 'tima' which could be a Ultima reference. A parody of Asahina, Mikuru from The melancholy of Haruhi Suzumiya (Pose "Mikuru Beam" and maid outfit).

She also appeared on episode 50 as a host of the quiz game, and appears on the inner cover comic (the one under the dust jacket featuring Nadja Orumuzuto) of Volume 13. (Source: Wikipedia)