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She is a caracter from Date a Live series.
As Mana's memories were starting to flash to her like a camera shutter, she briefly managed to catch a glimpse of Mio's appearance, describing her as a girl with long hair.
She is The First Spirit to make an appearance on 30 years before the beginning of the events in Date A Live, also known as the Spirit of Origin. She was summoned into the world by Sir Isaac Ray Pelham Westcott, Ellen Mira Mathers, and Elliot Baldwin Woodman through the Spirit Formula gathering all the world's mana into a single point. However, her birth also caused the first spacequake in history at some point of the frontier between China and Mongolia, killing over 150 million people and starting a chain of similar disasters around the world that would last approximately six months.
It's revealed that Mio has a doppelganger which is the Reine Murasame.