Medusa Gorgon is a powerful snake witch and one of the central antagonists in the series. She is a brilliant but cruel scientist whose primary obsession is the evolution of Black Blood, a substance that amplifies madness and destructive potential. Her background reveals that she is the mother of Crona, whom she uses as a test subject for her experiments rather than raising as a child. To advance her plans, she infiltrates the Death Weapon Meister Academy by posing as the school nurse, a disguise that allows her to study the students and manipulate events from within.

Her personality is manipulative, sadistic, and deeply calculating. She views people—including her own son—as convenient tools or experimental subjects rather than individuals with their own worth. She takes genuine pleasure in exerting control over others and is willing to use any means necessary, including planting snake bombs inside fellow witches to force their cooperation. Her mindset is similar to that of Dr. Franken Stein, seeing the world and everyone in it as an ongoing experiment.

Medusa’s primary motivation is a desire for chaos and power. Dissatisfied with the stagnant state of the world, she seeks to awaken the Kishin, Asura, the god of madness, believing that his release will force evolution through upheaval. She is also driven by a personal ambition to surpass other witches, particularly her older sister Arachne, whom she later targets directly.

In the story, she functions as the main architect behind the plot to free Asura. She manipulates Crona into collecting souls and becoming a vessel for the Black Blood, and she carefully orchestrates the events that lead to Asura’s resurrection. Her infiltration of the academy allows her to observe potential threats and allies. She engages in a climactic battle with Dr. Stein in the lowest levels of the school, where she initially has the upper hand but ultimately loses due to overconfidence; Stein cuts her in half. However, a snake containing her consciousness escapes, and she survives by possessing a young girl named Rachel. Later, she obtains the legendary artifact BREW and leads a group of students in an attack against Arachne, showing her relentless pursuit of power.

Her key relationships are defined by manipulation and rivalry. With Crona, she is abusive and exploitative, implanting a hypnotic spell to force the child to fight and kill. With her sister Arachne, she is antagonistic and willing to betray family to achieve her goals. She also has a complex dynamic with Dr. Stein, whom she tries to seduce and manipulate but also respects as a worthy opponent. Her development is minimal in terms of redemption; she remains consistently self-serving and villainous throughout, adapting to survive and continuing her schemes after her apparent defeat.

Medusa’s notable abilities revolve around snake-themed magic. She can summon and control thousands of snakes from her own body for offense, defense, and reconnaissance. She uses vector arrows—geometric, arrow-shaped constructs—that can strike at range or manipulate physical objects. Her hypnotic spells allow her to dominate others’ wills, as seen with Crona. She can create snake bombs that burrow into other witches’ bodies, letting her monitor or control them without dropping her soul protection, which prevents magical detection. Her soul itself takes the form of a snake, further reflecting her thematic connection to serpents. She is also a master of deception, capable of maintaining a calm, supportive facade while hiding her true, ruthless nature.