Miwa is the younger sister of Machi. She is initially introduced as a schoolgirl with a forceful personality who occasionally helps Machi and Amamiya in their cases. As the series progresses, she becomes more important as revelations about her role in the conspiracy that runs through the book are revealed. She is later revealed as a new generation bar-coder who carries a crucial alternate personality for the formation of Lucy Monostone. Her last seemingly important role was to transfer the personality of Kazuhiko Amamiya to Nishizono Tetora.