Mateo is a shy, kind eighteen-year-old boy who struggles with anxiety. Throughout the novel, Mateo demonstrates the value of making living life to the fullest a priority. With the help of his foil and Last Friend Rufus, Mateo is able to confront and defeat the fears that have always held him back. From leaving his apartment and trusting Rufus, to riding on Rufus’s bike and singing in public, Mateo transforms. His most significant change is in coming out as gay and expressing his love for Rufus before their time runs out. Mateo also demonstrates the importance of kindness and a concern for others. Upon getting the news from Death-Cast, Mateo’s first thoughts are to make sure to leave the apartment tidy for when his father comes home from the hospital, and he continues to consider his father’s feelings throughout his End Day. When Mateo takes time to bury a dead bird, he shows that there is value in every life. Similarly, he encourages Rufus to value himself and make peace with his survivor’s guilt. When Kendrick is about to attack Mateo at Clint’s Graveyard, Mateo’s past act of anonymous kindness prevents Kendrick from hitting and potentially killing him. Mateo’s final action in the story is to make tea for himself and Rufus, showing that although Mateo changes dramatically throughout the novel, his kindness endures.