Shuuji Fujigawa

A childhood friend of Takumi Hijirihara and one of the two survivors of the Giboura Massacre which turned Takumi into the Killer Killer. After discovering this, he became passionate about helping his friend understand the horror of murdering and make him drop this Killer Killer persona.

Similarly to Takumi, Shuuji is very fond of cramped spaces— so much so that he does not even have a bed and prefers to sleep inside a locker. He likes to present himself as a calm and collected individual. He cares greatly about Takumi and focuses on stopping Takumi from being a killer. Shuuji has no respect for killers and will put the extinction of all murderers above human lives.

Later, it is revealed that Shuuji is the first and official bearer of the title Killer Killer (キラーキラー).

(Source: Danganronpa Wiki)