Duchess Morbucks (known also as Miko Shirogane in Japan) is the older sister of Princess. Her younger sister envies her accomplishments and the attention her parents give her, but the two have a close relationship, nevertheless.
In the episode, "The Mighty Morbucks" ("Demashita! Shigoraine Z"), Duchess came to vist Princess from London and when Princess told her about the Powerpuffs, she swore to help Princess get revenge on them for outshining the Morbucks. She struck a deal with Mojo Jojo to attack the girls and as the fight happened, she made her family scientists contruct a super-outfit using abilities and weapons similar to the Powerpuffs' own as part of a plan to steal the attention away from them. Under the guise of "Shirogane Z", she fought the Powerpuffs and was able to counter all of their attacks with her powers. However, she could only use these powers under a three minute time limit. Though she didn't beat the girls, Duchess still yet had the last laugh when she had the filmed footage of her fight with them edited to make it appear as if she had rescued the girls from Mojo, which humiliated them when it was shown on TV. Duchess returned back to London at the end of the episode.
She made an unspeaking cameo appearance in the final episode.