Shingo Sumeragi is Matoi Sumeragi's father and a police detective. He lived separately from Matoi for several years due to his demanding career; during this separation, following her mother's disappearance, she resided with her grandparents. Their relationship is initially strained, reflected by Matoi addressing him by his first name.

Shingo's investigation commences after an attack damages Tenman Shrine, where Matoi works part-time, and injures the Kusanagi family. He apprehends a disturbed individual who serves as the sole witness to this incident. This confrontation coincides with a ritual performed by Yuma Kusanagi, inadvertently triggering Matoi's transformation and granting her divine powers. Unaware of his daughter's abilities, Shingo continues investigating supernatural disturbances in Kamaya City, particularly attacks by malevolent spirits called "Nights." His investigative rigor often conflicts with Matoi’s efforts to conceal her secret identity, creating tension as he pursues leads related to the attacks.

Throughout the series, Shingo actively pursues reconciliation with Matoi. He expresses consistent concern about his parenting shortcomings and strives to understand her experiences, demonstrating commitment to their familial bond. His investigative path occasionally intersects with the broader conflict involving secret organizations like IATO and Fatima, though he remains largely unaware of their operations or Matoi’s direct involvement in combating the Nights.