Throughout the story, the black flag represents a warning of something dreadful to come and a signal of upcoming disappearance. In olden times, a Kurohata, or black flag, was used to signal the spread of infectious disease within a town, warning travelers away. Hata’s adoptive family, the Kurohatas, descend from prominent apothecaries who would venture into infected lands to treat those who lived within. Captain Ono uses the black flag as a signal to Hata to remove K from service and examine her for infection and disease. Captain Ono orders Hata to prepare, treat, and isolate K beforehand by locking her in the surplus supply closet until he says otherwise. His decision to use a black flag as a signal to get her ready is intentionally belittling to Hata, while at the same time keeps others away from the infirmary. In reality, it is unusual that the doctor singles her out before any indication of an illness or malady, and his singular fixation on K is nothing other than sexual desire and infatuation. The day that Captain Ono hangs the flag outside the infirmary marks the day of K’s brutal murder, and Hata’s last chance to save her from whatever Captain Ono had planned for her.