Himeko Shirogane is a wealthy Tokyo City (New Townsville) middle school student transformed into a recurring antagonist after exposure to a black Chemical Z-ray. This event grants her the ability to become the supervillain alter ego "Princess" (Princess Morbucks), triggered by her pet cat Sapphire's scream. She retains no memory of her actions upon reverting to her human form.

Her civilian identity displays spoiled arrogance, often taunting those she considers lower class. This stems from familial neglect; her parents consistently favor her accomplished older sister Miko (Duchess), leaving Himeko craving recognition. Her jealousy fixates on the Powerpuff Girls Z, whom she views as rivals for attention, though she has no desire to join their team.

As Princess, she executes technology-driven schemes to undermine the Powerpuff Girls Z, constructing destructive robots and weapons to stage heroic scenarios for herself. Her motivations primarily seek validation rather than stem from inherent malice. Across the series, her character shifts from outright hostility towards the heroes toward occasional, reluctant cooperation, including later collaborations with her sister Miko during confrontations, reflecting evolving familial dynamics.

Her human form features orange hair and red eyes, shifting to red hair and hypnotic yellow eyes when transformed. As Princess, she wears a mauve and purple minidress with black stockings and red Mary Jane shoes. Her abilities include flight and the creation of advanced weaponry, centered on technological prowess.

A two-volume manga adaptation briefly features Himeko, focusing on her civilian interactions and rivalry with the heroes.