Master is a female employee of the Horse's Bone bookstore.

She received her nickname "Master" when she first announced to the others her dream of surpassing a master mangaka one day. Master is actually a doujinshi mangaka in her spare time, drawing and writing under the pen name Jona Taro - who Umio is a big fan of.

Appearance-wise she wears glasses and has long black hair. She lives alone in an apartment.