Kyoko Karasuma is a 16-year-old police inspector from Asakusa, Tokyo, Japan. She may be young but still considered one of the best inspectors of Asakusa, being a member of the special Security Division of Tokyo Police Dept. This division was created to hunt and kill—if not slaughter—people who have horns on their heads.
Kyoko, as a police inspector, has a rather cold personality. On the ground, she rarely smiles, nor is happy from exterminating Oni. She was raised as a child by her mentor and chief, Kozo Mitamura, and she owes him everything. Despite her young age, everyone in the bureau acknowledges her as the best inspector of the Dept. When she's not in charge of an affair, she is very calm and serene.
Kyoko is the descendant of one of the two greatest Oni Families, the Karasuma Family. Her father was killed 20 years ago by Kozo Mitamura. At the time, he was a member of a special Division named "Maruki," who was created to exterminate Oni. Eventually, he found Kyoko's family and killed her father (an Oni) because he was forcing Kyoko's mother to marry him. Mitamura developed feelings for Kyoko's mother, and that's the reason why he didn't kill Kyoko: she looked a lot like her mother.
Eventually, Kyoko encounters an Oni called Kirio Uchida, a member of the Uchida family, the other great Oni Family. She learns from her first duel with him that she is an Oni of a great descendent. From that time onward, she begins to crumble and lose her confidence.