Kirei Kisegawa is a supporting character at Ninjutsu Gakuen, initially presenting as the protagonist's friendly and cheerful classmate. She maintains a bubbly, positive facade as the group's mood maker, displaying notable fearlessness by openly associating with the protagonist despite antagonistic threats. Her appearance features long blonde hair styled in a single pigtail reaching her skirt length, worn with the standard school uniform.

A pivotal character development reveals her hidden allegiance at the end of Episode 5. Kirei is exposed as a spy for the Koga clan, operating under Suzaku Ban's command as a member of the Fuma ninja faction. This revelation shows her nervous and subservient demeanor towards Ban, whom she addresses as "Master" while pleading for mercy and following his orders. Her confident persona shifts markedly to apprehension during her covert role.

Hailing from Fuma Village, Kirei belongs to a faction characterized by conservative and radical ideologies. The Fuma clan disapproves of ninja modernization, preferring traditional methods, and seeks to provoke conflict between the Iga and Koga clans to weaken both through prolonged warfare. Her dual identity positions her as a deceptive manipulator within the narrative, cloaking her intelligence-gathering mission for the Koga behind a facade of friendship.

Her name, Kirei Kisegawa, reflects her character: "Kirei" combines the characters for "brightness, radiance" (輝) and "beautiful" (麗), while "Kisegawa" incorporates "yellow" (黄), "swift current" (瀬), and "river" (川).