The Otome of the Harmonium is a figure in Mai-Otome who operates the device known as the Harmonium.

The first Otome of the Harmonium, working at the time of the War of Twelve Kingdoms, was likely Fumi Himeno, the founder of Garderobe. At this time, the Harmonium was responsible for the destruction of much of the world, as well as the "curse" which afflicts the Aswad, the last survivors from the people of the Black Valley (which also disappeared at that time into the Sprites' Forest) and their descendents.

The second Otome of the Harmonium, operating 300 years later in A.R. 330/331, was Nina Wáng, working for her Master Nagi Daí Artai. At this time, the Harmonium was used to destoy a variety of places (Albright Base in Aries, Florince's Boldoor District and Anmilla District in Lutesia), as well as the more humane purpose of keeping alive the grievously injured Sergay Wáng.