The EOs of Vicious are both a motif of the book, as well as a commentary on superhero fiction and comic book tropes. Throughout the book, the existence and powers of EOs allow for speculation on the book’s major themes, as well as a glimpse at what reality might look like in a world populated by EOs. In superhero fiction, lines between good and evil are often finely drawn. Superheroes like Superman and Batman are firmly on the side of good, where as their nemeses (Lex Luthor, the Joker, etc.) are defined as evil. Vicious subverts these tropes, offering morally gray EOs who possess qualities of both heroes and villains.

In the world of Vicious, EOs are made as the result of a traumatic brush with death. Eli and Victor speculate on the qualities required for a person to become an EO, and while they never settle on a specific formula, they agree that the circumstances of death must be traumatic/violent and there must be a desperation to live. The four main characters of the book show this type of experience in two different ways. Victor and Eli induced their death experiences, purposefully putting themselves in physically traumatic situations in an attempt to gain powers.