Setsuo Miyamoto

Setsuo Miyamoto is a minor antagonist in Fire Force. He is a former firefighter who became a serial killer, murdering several people (four, in most accounts) for his own amusement. During his trial, where he was on the verge of being acquitted due to an insanity plea, he undergoes Spontaneous Human Combustion and transforms into an Infernal.

Unlike typical Infernals, who lose their minds and act mindlessly, Setsuo retains his full self-awareness, intelligence, and sadistic personality because of his strong attachment to life. He goes on a rampage, taking advantage of his new powers, and is eventually defeated by Shinra Kusakabe. Afterward, he is captured and used for experimentation by Company 5.

As a human, he was described as a bald, middle-aged man with stubble and a devious look. He's one of the few truly villainous Infernals in the series, driven by cruelty rather than tragedy.