|This character exists primarily or exclusively within the Sonic X continuity.|
Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
She is the only E-00 series robot Doctor Eggman built with a female personality. She has many skills such as walking through walls and knocking characters out without touching them. She was defeated in the end when Hawk dumped water on her.
A robot based on a female ninja, E-91 was equipped with shurikens, gliders, an electrocution net, a chain with a weight at the end that could either be small or turn into a wrecking ball and an entire arsenal of different Ninjutsu techniques. Her name is a pun; the word "Kunoichi" means "Lady Ninja", but when the word is separated, it also means "91" (Ku-no-ichi). The Lady Ninja was dispatched to retrieve the red Chaos Emerald, but ran into trouble in the form of Knuckles the Echidna and Rouge the Bat. Eventually, she had Knuckles on the ropes, but Knuckles' human friend Hawk dumped water over her. Taking advantage, Knuckles hit her with a super punch, destroying her. Lady Ninja was 120 cm (4 ft) tall and weighed 200 kg (440 lb).
- Her head shape is similar to Bokkun's.