The "Boogiepop at Dawn" light novel describes how Dr Kisugi witnessed Nagi's remarkable recovery and, through experimentation on rats, learned of the drug's powers to grant superhuman abilities, before administering it to herself. The drug changed the doctor into a composite human, granting her the vast increase in physical and mental attributes shared with all composite humans and allowing her to sense the hormones that produce fear and develop a craving for them. At first terrorizing her patients and sampling their blood, she then murdered a number of strong-willed girls to consume the fear they produced at the moment of their death. "Boogiepop Phantom" shows how Dr Kisugi gave the drug to her patients, claiming it could heal them, and how it worsened their problems and resulted in their evolution. Kirima investigated the murders, and discovered Dr Kisugi was the serial killer. Nagi and Dr Kisugi confronted each other at the hospital, where The Fire Witch was initially overwhelmed by the doctor’s power, but managed to kill her with Boogiepop's help.