Keto is a supporting character in The Duke of Death and His Maid. She is a witch with blonde hair and dark skin, who appears wearing a swimsuit. Her visual presentation is frequently compared to a gyaru, a Japanese subculture associated with a fashionable and carefree attitude.

Keto is a subordinate of Daleth, a powerful witch and leader of a group. She is rarely seen alone and is almost always accompanied by Teto, another witch with whom she shares a close romantic relationship. The two are a couple and act as a pair consistently throughout the story. Keto also follows Daleth on missions; for instance, she and Teto accompany Daleth when she goes to the human world to recruit the magician Zain.

Her magical specialty is plant manipulation. She excels at magic that allows her to control existing vegetation and can even cause new plants to appear at will. Keto is not hesitant to use her abilities offensively, once sending a plant vine to attack Alice and the Duke during a confrontation at a witches' gathering.

Her personality is deeply influenced by a philosophy she embraces called gyaru mind. This outlook means she does not hold long-term grudges, even against her enemies. Her speech pattern is casual and distinctive, often ending her sentences with the suffix ssu.

Keto's motivations and worldview have been shaped by her past. Having lost many of her fellow witches in historical witch hunts, she does not hold a favorable opinion of humanity in general. However, she demonstrates a strong sense of loyalty to her leader, Daleth. If Daleth decides to pursue a path of reconciliation with humans, Keto is prepared to set aside her personal feelings and follow that will.