Madame Ko was Domovoi Butler and Juliet Butler's bodyguard, tutor, and sensei. She is Japanese and owns an Academy which commonly moves around to protect the safety of the bodyguards training there. Graduates all receive a trademark blue diamond tattoo. She is known for her cunning and testy tricks.
In Juliet's final bodyguard test, Madame Ko substituted herself for a petite Asian girl to take her place in order to trick Juliet. When Juliet ran in to save "Madame Ko," she grabbed onto a clothesline, brought the loin's cloth and wrapped it around the "attackers." After incapacitating the targets, Juliet excitedly ran up to "Madame Ko," exclaiming to her teacher that she did a good job. However, "Madame Ko" raised a knife to Juliet's neck. Then, out of the shadows, stepped the real Madame Ko. She said that Juliet was too impractical and reckless for being a bodyguard and wasn't suited for the seriousness of bodyguard life.