Nikaidou is Kaiman's present companion, she owns the Hungry Bug, a family restaurant in The Hole.
Nikaidou found Kaiman after his initial transformation, and has befriended and aided him ever since. They, together, hunt down magic users who enter The Hole, and try to locate the one who inflicted the transformation on Kaiman.
As the story progresses, it is revealed that Nikaidou is also a magic user and has some ties in the Magic Users' World. It is later revealed her power is the control of time.
When she trains with the ex-devil, Kawajiri, she discovers that her magic can only be used a limited amount of times before eventually becoming completely unusable.