Mateo is a skinny, 18-year-old Puerto Rican teenager, who, for most of his life, has led an isolated existence, preferring to spend his days indoors playing video games and browsing online. Mateo is virtually alone on his End Day, as far as family is concerned: Mateo’s father is in a coma after an embolic stroke, and Mateo’s mother died giving birth to Mateo. Over the course of his End Day, Mateo goes through a transformation: At the start of the day, he is paralyzed by fear, but by the end of the book—with Rufus’ help and guidance—he finds the courage to take advantage of his final 24 hours alive and discovers his sexuality, as he finds himself attracted to Rufus. Mateo initially worries that he has not lived his life to the fullest, but by the end of the novel, he has learned to cherish and make the most of every moment. 

Rufus is a 17-year-old Cuban teenager, who is the antithesis of Mateo: Rufus is bold and courageous, and he eschews social media, preferring instead to live in the real world. Rufus’ parents and sister died in a fatal car accident, in which their family car tumbled into the Hudson River.