She is a character exclusive to the game Date A Live Twin Edition: Rio Reincarnation and the novel version of the game.
Rio has long plum hair that reaches to her legs. She ties her hair with one single braid and has a bow at the top of her head. Her eyes have a deep color. While in her Astral Dress, Rio wears a lavish pinkish-red dress with a gold emblem on the center. The dress also contains a large robe that reaches her feet.
She's the daughter of Shido and Rinne Sonogami.
She's the niece of Tohka and Ren and granddaughter of Mio Takamiya.