Kotaro Yanagisawa

Shiro is a mysterious man and former caretaker of Itona Horibe.

Appearance
Because Shiro wears white robes made out of anti-sensei materials and a mask over his face, his actual appearance is unknown. However, when he removes his mask in chapter 133, he is revealed to have short, wavy black hair and light eyes with his left eye being a prosthetic eye.

Personality
During his first appearance, he seems almost funny and easygoing, but as he continues to manipulate Itona into attacking Korosensei, his true colors were revealed to be much more conniving and manipulative. Furthermore, he sees practically everyone other than himself as disposable (a trait that he retained since being a researcher). In his past as a researcher, he was revealed to be quite arrogant, amoral, and abusive given how he was willing to use human guinea pigs for his research and constantly beat up Aguri Yukimura, his fiancee, and even fellow scientists for supposedly getting in the way of his research.

History
His history is mostly unknown, but he likely a large role in the creation/mutation of Korosensei. His real name is Kotarō Yanagisawa, chief scientist of the project that transformed Korosensei into a tentacle monster. He was noted by Korosensei as a genius scientist before the incident happens. It is revealed that he was a heir to a wealthy family and a genius biologist in charge of the world research foundation but was also revealed to have no ethics regarding his research whatsoever.

Itona Horibe
Guardian

Kaede Kayano
Brother-In-Law

Aguri Yukimura
Fiancee

Trivia

 * His clothing has shown to be of the same material that the 'Anti-Sensei' weapons are made from, as Kurosensei was unable to touch him without the offending area being destroyed.
 * He has been shown to have a device which emits a beam of light that paralyses Korosensei for a short period of time. Whether this works of Itona is unknown.