Shion was born to her mother Azami and her father Tsukihiko. As a child, she grew up with her father Tsukihiko while awaiting the return of her mother, who had disappeared into the Kagerou Daze. While she was waiting years for her to return her father died of age.[1] She continued to live in the forest even after Tsukihiko's death, and eventually had a child, Marry, with a human. Fearing that Marry could be threatened by humans because of being a Medusa's descendant, she decided to raise her daughter in the forest until she became an adult. Knowing that she couldn't protect her forever she wrote a diary to her to make sure Marry would know how much she loved her.[2]
One day Marry was attacked by humans, and Shion used the Medusae's power to "turn those she makes eye contact with into stone" to protect her. However the strain inflicted to her body by her eye powers was too great for her to bear, resulting in her death.[3]
She was dragged into the Heat Haze along with Marry, where she reunited with her mother. Although she was offered the "Combining Eyes" ability in exchange for replacing her life, she gave the ability to Marry and sent her to the outside world instead.