One is an integer who debuted in "X Finds Out His Value", and recommended character in the Battle for BFB episode "The Tweested Temple".
In "X Finds Out His Value", X finds out that his value is seven, which is considered to be a lucky number. One is seen watching Four and X with an angry expression on their face. Three, who is next to One, is also seen angry at Four and X, likely due to One and Three forming into a Thirteen, which is considered an unlucky number, and grunts.