The following is a list of characters for the Yu-Gi-Oh! anime series, Yu-Gi-Oh! Zexal and its sequel, Yu-Gi-Oh! Zexal II. Where appropriate, names from English-language anime are on the left, while the original Japanese names (used in Volume 1 of the English-language manga) are on the right. Character descriptions pertain to the Japanese version of the anime.
Introduced to the series are Xyz Monsters, which have also been added to the Yu-Gi-Oh! Trading Card Game. By stacking two or more monsters of the same level on top of each other, an Xyz Monster with a Rank that matches that level can be summoned. The overlaid monsters, or Overlay Units, can then be used to activate an Xyz Monster's effect. The most prominent Xyz Monsters in the anime series are the Numbers cards, some of which have Chaos Numbers counterparts.
This is simply new terminology for an old mechanic: the mechanic in question requires a player to sacrifice monsters in order to activate certain effects. When a player sacrifices a monster, he or she is now said to tribute them: an example is tribute summon, where Level 1-4 monsters are sacrificed or paid as tribute to summon stronger monsters such as Galaxy-Eyes Photon Dragon and Jawsman. Number monsters could also be tributed.