Hannah Stein is a fictional character from the anime The Darwin Incident. She is the human foster mother of Charlie, the half-human, half-chimpanzee protagonist known as a humanzee. Hannah, alongside her husband Gilbert Stein, is a chimpanzee researcher by profession. The couple adopts Charlie immediately after his birth, which takes place during a raid by an eco-terrorist organization. They raise him in seclusion for the next fifteen years, providing him with a loving and protective home environment away from the outside world.

As a character, Hannah Stein is defined by her role as a devoted and nurturing parent. Her primary motivation is the well-being and safety of her adoptive son, Charlie. She is determined to give him as normal a life as possible, despite his extraordinary origins and the dangers that surround him. This determination manifests as a persistent effort to treat and engage Charlie as a typical teenage boy, even going so far as to have awkward but well-meaning conversations with him about his friendships and social life, such as his relationship with his first human friend, Lucy Eldred. Her efforts, while coming from a place of deep love, sometimes highlight the fundamental differences between Charlie and other humans, underscoring the unique challenges of their family dynamic.

Within the story of The Darwin Incident, Hannah serves as a crucial pillar of support and a representative of Charlie's personal, human-connected life. Her home is the sanctuary from which Charlie ventures into a hostile and curious world. Her relationship with Charlie is the central familial bond that motivates his actions, as his determination to fight back against the terrorist group, the Animal Liberation Alliance, is explicitly stated to be for the sake of his loved ones, which includes his foster parents. Her key relationship is with her husband, Gilbert, as together they form the core family unit that shelters Charlie. There is no information available about any notable abilities possessed by Hannah Stein, nor is there substantial information regarding her personal development or any evolution of her character role throughout the series.