Shiro

Shiro (real name kotarō yanagisawa) is a mysterious man and former caretaker of itona horibe. He is a recurring antagonist to class 3-e in the first half of the series, but later serves as the final antagonist. Shiro wears white robes and a mask over his face, all made from anti-sensei fibers. His actual appearance was unknown until he removed 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.

This chapter also revealed that he used voice changing technology to hide his identity from korosensei. During his first appearance, he seems funny and easygoing, and although he retains this attitude while he and itona attack korosensei, it soon becomes clear that he is conniving, manipulative, and ruthless in his ambitions.

Furthermore, he sees practically everyone other than himself as disposable. In his past as a researcher, he was revealed to be quite umempathetic; he was willing to use human guinea pigs for his research and took out his anger on his coworkers and subordinates, including his fiancee aguri yukimura, for getting in the way of his research. Because of his personality, koro-sensei exploited it twice for his advantage before he was completely defeated as he was abandoned by many country leaders after his defeat in the final battle between yanagisawa, god of death and koro-sensei.