Nanase is Hoichiro Ohma's girlfriend and colleague at their shared workplace. She views him as quiet and humble, entirely unaware he secretly operates as the supernatural "Judge of Darkness," delivering justice to criminals beyond human law.

Their realistic, romantic relationship involves a shared domestic life. This domesticity creates moments of levity, such as their supernatural parrot mimicking sounds from their private moments, leading to awkwardness the following day. Nanase primarily serves to contrast Hoichiro's dual existence, grounding him in ordinary human connection without knowledge of his clandestine activities.