Kyoko Esumi is a main character and a student at Hanazuka Prefectural High School, where she is a classmate of the protagonist Hibiki Amami. Her background is marked by a stark contrast between her present and her past. Before the events of the story, she was a notorious and legendary delinquent known as the Scorching-Haired Savior or Flame-Haired Messiah, a reputation she earned for protecting the weak and confronting the strong. This period of her life is a source of deep personal embarrassment, and she generally wishes to forget it, becoming angered whenever someone brings it up. A specific spiritual encounter during her delinquent days, where she helped an earth-bound spirit, contributed to a significant aspect of her character: an intense and profound fear of anything related to ghosts or the supernatural.

Despite her tough exterior and rough personality, Kyoko possesses a very soft and compassionate heart. She has a powerful sense of justice and cannot ignore anyone in trouble, a trait that remains with her from her days as a protector. Within her group of friends, she often acts as a dependable big-sister figure and a natural-born leader, serving as the grounded, straight-talking member who keeps the team focused. This often manifests in her being the first to physically admonish the more eccentric members of the group, such as Kenta Yamada, when they act in a foolish or perverted manner. Her tough demeanor, however, masks her genuine care for her friends and her secret vulnerability regarding ghosts, which surprises others who see her as calm and laid-back.

Kyoko is the childhood friend of Kana Uehara, and the two share a strong bond, knowing each other's dark pasts. Her role in the story often involves acting as a protector for her friends, particularly in situations that might involve the supernatural, despite her own fear. She serves as a foil to both Hibiki, who is friendly and open with ghosts, and Kana, who is more accepting of the paranormal, by representing a more normal and fearful reaction to spirits. Her motivation is largely driven by loyalty to her friends and her innate desire to help those in distress, whether it involves defending them from mundane troubles or, reluctantly, supporting them through supernatural encounters. While Kyoko does not possess any spiritual abilities herself, her notable abilities are her physical strength, combat prowess, and fearless attitude when dealing with human threats, all remnants of her days as a legendary delinquent. Her development throughout the series involves her slowly reconciling her frightening past with her present life and learning to cope with her fear of ghosts for the sake of her friends.