Sayoko Onigahara

Sayoko Onigahara (鬼ヶ原小夜子, Onigahara Sayoko) is one of the prisoners in the Haguro Prison. Her inmate number is LB0003. Her "base" is that of a Schutzstaffel, Josef Mengele.

Appearance
Sayoko is a young beautiful girl with long black hair and straight bangs, with a white headband separating her bangs with the rest of her hair. She wears the Haguro uniform when inside the prison. When she gets taken over by her "base" Josef Mengele, Sayoko sports a Schutzstaffel-style Nazi soldier outfit, with a long white coat and a Nazi hat. She usually carries a rapier with her in this form.

Personality
Sayoko is confident and calm at most times, and cautious with most people, but she was friendly with Chika as shown in their first encounter. When in her Medusa form, she sports a murderous and calm demeanor, and is shown to be intelligent and possess a tactical mind, ruthless and sadistic when torturing her enemies, as she only treats them as experimental subjects.

Background
It is said that Sayoko committed many murders in Tokyo. Especially, she liked removing her victims' brains. Many of her victims were said to be mature women. Sayoko claimed that she lost her parents at a young age. Thus, she inherited their fortune. After selling a land which was her family's legacy, she got lots of money because of it.

Sometime before the arrival of Miina Isurugi, she got along with her cellmate and the previous owner of bracelet #8, Sara Sunagawa. She then killed Sara and removed her brain. In Chapter 46, it is hinted that she was not aware when she killed her due to Medusa Syndrome.

Abilities
Her murder model, Josef Mengel, was a physician-scientist that performed deadly experiments on humans during WWII, explaining Sayoko's adept knowledge on physics, science, and chemical properties and her applications of using them to her advantage. She relies mainly on her wits and knowledge rather than physical strength (only using the rapier for attacks such as a stealth one on Karen during Chp. 26).

She can design the battlefield to her advantage, such as setting up gases to poison or immobolize her enemies, like she did in Chp. 24 with Tomoe Aya, Kirishima Karen and Isurugi Miina, albeit it was a failed attempt and they recovered shortly afterwards. Sayoko also possess knowledge on facial geometry, as she could see the patterns of the facial muscles on Miina and Chika in Chp. 24, and demonstrates precise accuracy of the facial details based on the golden ratio.