Minatsuki Takami is a supporting character in the story, known within the prison complex by the codename Hummingbird. She is the younger sister of Yoh Takami and is classified as a Deadman, a prisoner who possesses a Branch of Sin, a supernatural ability that allows them to manipulate their own blood. Before the catastrophic earthquake that devastated Tokyo and triggered her transformation, Minatsuki was an ordinary girl. During the earthquake, she was trapped in a greenhouse. When her mother came to rescue her, her mother instead grabbed a plant and fled, abandoning Minatsuki. The entrance collapsed on her mother, killing her. Minatsuki was eventually saved by her brother, Yoh, but the trauma of being abandoned by her mother led her to develop a deep-seated hatred for humanity and a profoundly sadistic personality. This traumatic event also awakened her Deadman abilities, and she later used her power to kill her father.

On the surface, Minatsuki initially presents a facade of a shy, timid, and reserved young girl who claims to be terrified of violence and haunted by her past. This appearance is a deliberate ruse designed to lull opponents into a false sense of security. In truth, she is deeply sadistic and derives pleasure, even of a sexual nature, from witnessing the pain and suffering of others. She particularly enjoys seeing the look of guilt and self-blame on her brother's face regarding their father's death, even though Yoh knows the real truth behind the incident. Her motivations are rooted in this trauma and her resulting misanthropy, finding satisfaction in manipulating and tormenting those around her.

Her role in the story is primarily as an antagonist and a formidable opponent during the Carnival Corpse death matches within Deadman Wonderland. She is initially an obstacle for the protagonist, Ganta Igarashi, whom she targets with her deceptive tactics and cruel fighting style. Minatsuki's key relationships are central to her character. With her brother Yoh, their bond is highly complex and toxic, marked by her sadistic enjoyment of his guilt yet also tied to a deep, underlying familial connection. With Ganta, their relationship begins with her attempting to dominate and kill him in combat but evolves after she loses to him, leading to a strained and reluctant reconciliation.

After her defeat by Ganta, Minatsuki begins to exhibit signs of development. She reconciles somewhat with both Yoh and Ganta, though she still frequently lashes out at them verbally. This marks a shift from her purely antagonistic role, hinting at a potential for change and a struggle between her ingrained sadistic impulses and a buried desire for genuine connection. Her notable ability is her Branch of Sin, which is called Whip Wing. This power allows her to gather blood from her body and expel it from her ears, forming it into long, flexible, and razor-sharp whips. These whips can be used to strike opponents at a distance with great speed and precision, as well as to restrain them. However, using this ability requires a significant amount of blood, which can leave her physically drained and vulnerable if she overexerts herself in battle.