Medusa is a famous, or perhaps infamous, character in Greek mythology. She is one of the three Gorgon sisters, of which she is the only mortal one. A single glance of her terrifying eyes is believed to turn the onlooker into stone. Even after she was decapitated by Perseus, her head is said to retain its powers of petrification.
She is recognized as such a terrifying figure that her head is depicted on temples and buildings to protect them from evil spirits and thieves.
She is the boss of the floating city of Bien. Her shadow appears as a demon of the Foul race that attacks Nakajima as he advances through Bien. If Nakajima has obtained Tabasa's Statue, it will seal her Petrification attack, and will shatter after the battle. According to one NPC in the Valhalla Corridor, Medusa had Minotaur make her the Taurus Key so she could close off Bien.
"A monster of Greek lore; one of the three Gorgon sisters. She had snakes for hair, bronze scales for skin, golden wings on her back, sharp fangs, and eyes that could turn anyone who looked straight into them into stone. In some traditions, she was a beautiful woman, and her snake hair was her only ugly feature. With the help of the goddess Athena, Perseus was able to behead her."
—Shin Megami Tensei IV Profile
A demon found in the deepest depths of the part of Naraku that lies within the Unclean Ones Country on the 1st observation platform. The platform is filled with statues of her victims who she has turned to stone. Finding the prentice Samurai the most fascinating human specimens yet, she desires to add them to her collection and wants them to strike a pose while filled with fear. She begins to calling them Tayama's dogs carrying out orders as moles, leaving the prentices to believe she's losing her mind. She cries out for her body and its beauty as she crumbles and dies at the end of the battle.