Miwa Isono is the younger half-sister of Machi Isono. She lives with Machi in Tokyo and is introduced as a high school girl with a forceful, determined personality. She shares a close bond with her sister and initially appears as a supportive figure who occasionally assists Machi and detective Kazuhiko Amamiya in their investigations. Her motivations stem from loyalty to her sister and curiosity about the cases they encounter. As the story unfolds, Miwa becomes deeply entangled in the conspiracy surrounding the Gakuso organization. She is revealed to be a new generation bar-coder, a type of individual capable of carrying and transferring programmed personalities. This ability makes her a crucial component in the scheme to recreate the legendary killer Lucy Monostone. During a confrontation on an airplane, Miwa manages to absorb the personality of Kazuhiko Amamiya from Yosuke Kobayashi. Later, she meets Tetora Nishizono, another host of a Shinji Nishizono personality, and decides to transfer the Kazuhiko personality to him. She does so only after extracting a promise from Tetora that he will keep the Kazuhiko personality alive and safe inside him, no matter what. This act demonstrates her protective nature and her willingness to sacrifice her own connection to Kazuhiko for his preservation. In the live-action television adaptation, Miwa appears as a comatose girl rescued from a burning hospital who later develops a relationship with Amamiya. Her development moves from an ordinary schoolgirl into a key player in the larger plot, defined by her ability to host and transfer personalities and her deep loyalty to those she cares about.