Himeko Shirogane, who becomes the creature known as Princess, is a recurring antagonist in the anime. She is a thirteen-year-old girl from the immensely wealthy Shirogane family and attends the same middle school in Tokyo City as the three main heroines. Her life changed when she and her pet cat, Sapphire, were struck by a mysterious black light. This event did not grant her permanent powers but created a specific trigger for a monstrous transformation. Whenever Sapphire lets out a pained screech, often because Himeko accidentally steps on her tail or squeezes her too hard, Himeko transforms into her alter ego, Princess.

In this transformed state, her appearance becomes more flamboyant and aggressive. Her orange hair puffs out into a large red afro, her eyes shift from red to yellow with spiral patterns, and her white tights turn black. She retains her signature outfit, a puffy purple and lavender dress adorned with a large bow and a blue gem brooch, along with her tiny crown and burgundy Mary Jane shoes. A common comedic element is that whenever the Powerpuff Girls Z defeat Princess, they catch her in a giant purse, to which she calmly responds, "yes, okay," before reverting to her human form with no memory of her actions as a monster.

Unlike her counterpart from the original American cartoon, this version of Princess does not wish to become a member of the superhero team. Her primary motivation is a deep and desperate need for attention and recognition. This stems from her difficult family life, where her parents consistently favor her older sister, Miko, who is more talented and receives all their praise. This neglect has left Himeko feeling unappreciated and jealous, and she lashes out at anyone who draws the spotlight away from her, especially the popular Powerpuff Girls Z. Although she is spoiled and often acts arrogant toward those she considers lower class, her actions are driven more by emotional insecurity than pure malice.

In her civilian life as Himeko, she is a snobbish but not entirely unkind student. She has two close friends, Fumika and Hanayo, who act as her entourage. Despite her jealousy, she shares a complex but caring bond with her older sister Miko. In one instance, she even supported Miko when she tried to upstage the Powerpuff Girls Z as the hero Shirogane Z. Himeko is also suspicious of her three classmates who secretly are the Powerpuff Girls Z, often trying to catch them skipping class, though she never succeeds in uncovering their secret identity. Over time, her initial strong hatred for the trio softens, and she becomes somewhat friendlier toward them, even showing genuine concern for one of the girls' feelings on occasion.

As Princess, her abilities are directly linked to her desire for recognition. She possesses basic superhuman skills similar to the Powerpuff Girls Z, such as flight and enhanced strength. However, her most notable power is her ability to produce virtually any item from a kind of "hammerspace," including a diamond claw, a rocket launcher, or large sums of money. She frequently builds giant robots and other advanced technology to stage scenarios where she appears to be a hero, hoping to win the public's adoration. Her powers and even her hairstyle can fluctuate depending on special collars placed on her cat Sapphire. In one episode, she also demonstrates the ability to breathe in space. Despite her efforts, her plans are always foiled, and she is inevitably defeated by the Powerpuff Girls Z, reverting back to Himeko with no memory of her destructive alter ego.