Nanami Tokou is a magic user in the story who carries the research number 5210. Her official ranking is AA+, placing her among the more powerful artificially created witches. She is soft-spoken by nature and has a noted fondness for sugary foods. Nanami works as an operative for the secret organization Vingulf, and she initially appears as a minor antagonist tasked with tracking down witches who have escaped from the laboratory. However, her true intentions are more complex: she secretly extends protection to the main characters and quietly works toward her own escape from the organization's control.

Her defining ability is memory manipulation. By making eye contact with someone, Nanami can scan, modify, or erase their memories up to a certain depth. This power makes her a dangerous opponent, but it also carries a limitation that others can exploit by covering their eyes. She is frequently accompanied by a companion named Kurofuku, who wears sunglasses to stay safe from her power.

In terms of appearance, Nanami is a slender girl with purple hair tied into two braids and deep blue eyes. Her typical outfit is a black dress with white ruffles and a white collar.

As the story progresses, Nanami develops a respect for Ryouta Murakami's sharp observational skills. After her physical body is destroyed when her harness is ejected, she does not truly die. Instead, she survives as a disembodied consciousness that takes up residence inside Ryouta's mind. From this vantage point, she is able to manifest and assist him during critical moments, demonstrating that her loyalty has shifted from the organization to the people she has come to care about. Her arc moves from a seemingly cold operative to an ally who sacrifices her physical form yet continues to aid the protagonists from within.