Shiori Sumeragi is the wife of Shingo Sumeragi and mother of Matoi Sumeragi. Her disappearance years before the series' main events led Matoi to live with paternal grandparents until reuniting with Shingo. This absence deeply affected the family, particularly Matoi's longing for a normal life.

A decade prior to the story, Shiori heroically ascended to the 24th dimension to halt the dimension-merging Cavitas phenomenon. She transformed into a dimensional gate to seal the Cavitas, remaining there for ten years to prevent universal collapse, believed missing or deceased during this time. A protective charm she gave Shingo later saved him from demonic possession.

Shiori possessed shrine maiden abilities, including extrasensory perception to detect higher-dimensional beings, teleportation across dimensions via the Gate of Caelum, force field creation, and entity banishment. Merging with a higher-dimensional being during her sacrifice granted her reality-warping capabilities to maintain the seal.

She bears a notable physical resemblance to Matoi, especially when Matoi uses her exorcist form, causing Shingo to initially mistake Matoi for Shiori. Matoi eventually rescues Shiori from the 24th dimension, reuniting the family. After her return, Shiori resumes life with Shingo and Matoi, affectionately doting on Matoi. While Matoi initially believed her exorcist powers vanished after the rescue, Shiori's influence or legacy implicitly persists as Matoi's abilities resurface to fight supernatural threats alongside Yuma Kusanagi.