Character:
Medusa is a witch, who infiltrates DWMA under the guise of a kind nurse to awaken Asura and continue her research on the black blood. She is Crona's mother, and through years of abuse and research, she infuses Crona with the black blood and Ragnarok, and manipulates Crona into a ruthless killer. She often claims to care for Crona, though she simply views Crona as a tool to expend at any point. She sees the world as a giant experimentation ground, which is what causes her to awaken Asura. She is killed by Stein, whose similar personality interests her, but she manages to scatter her soul and reform it into a snake. Afterward, she possesses a young girl named Rachel and uses "Brew" as leverage to form a truce with DWMA.
Source from Wikipeida
