Kiri Nikaido is an agent of the Supernatural Disaster Countermeasures Division, serving as the personal assistant to her superior, Ayame Jinguuji. Within the organization, she has a serious and dedicated work attitude, showing unwavering loyalty to Ayame. In contrast to Ayame's friendly and relaxed demeanor, Kiri acts as a strict disciplinarian and is quick to scold anyone who disrespects her boss, giving her a harsh but principled reputation. Her primary role is that of a support staff member and guardian to Ayame, handling logistics and ensuring her safety. Following the traumatic events involving Yomi, Kiri undergoes a significant psychological change; she becomes mentally regressed and childlike, addressing Ayame as "onee-chan," which means older sister. While specific combat abilities are not her primary focus, she is shown using modified suitcases and strings as part of her duties as an agent. Her key relationship is with Ayame Jinguuji, whom she serves with fierce loyalty and later develops a more dependent, sisterly attachment to after her mental breakdown.