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.

History
His history is currently unknown, but he likely played a large role in the creation/mutation of Korosensei. His real name is Yanagisawa, and it's possible he is related to Kayano. He was noted by Korosensei as a genius scientist before the incident happens.

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.