Himiko Kudou, also known by her alias "Lady Poison," is a sixteen-year-old operative who works for the Transport Service known as the Hakobiya. She is recognized as one of the best in her field, known for making deliveries by any means necessary and without asking questions, a role she takes with intense seriousness and personal pride.

Her past is deeply intertwined with Ban Midou, a fact that defines much of her early demeanor. She was raised by her older brother, Yamato Kudou, and during her childhood, Ban came to live with them for a period of about six months. The idyllic relationship ended in tragedy when Himiko returned home one day to find Ban standing over her brother with his hand covered in blood. Ban never denied killing Yamato, though he could never explain why, leading Himiko to swear an oath of revenge against him. Far more than a simple murder, the truth was a tragic consequence of a mystical condition known as being a "Voodoo Child." Yamato was afflicted with this curse, which split his being into two halves with opposing natures; if one half died, the other would perish as well. In a fatal misunderstanding, Ban's "Snake Bite" ability killed Yamato's other half, inadvertently causing the death of the brother Himiko knew. Ban carried the weight of this promise to Yamato, a secret that fueled Himiko's misunderstanding for a long time.

This history of betrayal made Himiko fiercely independent, cold, and hesitant to form close bonds with others. She lives by the cynical belief that friends will ultimately betray a person and leave them to die. This emotional wall is a defense mechanism, born from the fear of being hurt again after losing her brother. Even when Ginji Amano offers her a chance to join the Get Backers, she refuses, preferring to keep a physical and emotional distance from people. Despite her tough exterior, she is also a feisty young woman who hates being treated like a child or having her age referenced. Her feelings toward Ban are a complex mixture of her sworn hatred and lingering affection from their past friendship, a conflict she struggles to reconcile as she learns more about the circumstances of her brother's death.

As a member of the Transport Service, she often works alongside formidable individuals like Akabane "Dr. Jackal" Kurodou and Maguruma. Her operational role frequently places her as a rival or reluctant ally to the Get Backers, allowing her path to cross with Ban and Ginji repeatedly. Her key relationship remains with Ban Midou, who views her more like a little sister, teasing her with nicknames like "washing board". This dynamic shifts over time as Himiko begins to see Ban in a more favorable light and uncovers facts about the Voodoo Child curse, eventually leading her to come to terms with the past and join forces with Ban and his companions.

Himiko undergoes significant development throughout the series. She is eventually revealed to be a "Voodoo Child" herself, a victim of a curse set to activate on her seventeenth birthday. This curse marks her as a reincarnated witch, making her one of the keys to unlocking the mysterious Babylon City. In a pivotal turn, she is forced to confront her mirror self, a being of opposite emotions. The resolution sees the two merging into a single body, unlocking her latent powers. Though she is initially believed to be dead, the event leads to her revival and deepens her connection to Ban, as it is eventually revealed that they are actually related by blood through the Witch Queen.

Himiko's primary abilities revolve around her mastery of poisons, for which she has earned her "Lady Poison" moniker. She is a witch who uses seven distinct poison perfumes to attack her enemies or enhance herself. Each perfume has a unique effect. For example, the Flame Perfume allows her to breathe fire by burning targets from the inside out, while the Corrosion Perfume acts like a potent acid. The Puppet Perfume allows her control over an inhaler's movements, and the Oblivion Perfume erases the last twenty-four hours of memory. Her most dangerous tool is the Acceleration Perfume, which drastically increases her speed but is life-threatening if used more than a couple of times. She also has access to a Trailing Perfume for tracking and an Antidote Perfume to neutralize her own toxins. As a Voodoo Child, she possesses latent magical power and can become a formidable adversary, sometimes relying on sheer strength and magic rather than her perfumes. A critical aspect of her technique is that the perfumes act as "catalysts" to evoke specific magical spells, a method of magic that differs from Ban's innate abilities.