Dox, known as Kyû in the Japanese version, is an opponent in Yu-Gi-Oh! Nightmare Troubadour. This is a videogame depiction of Dox, a character from the Yu-Gi-Oh! anime and manga.
Dox first appears at night, challenging the player to their first Shadow Game. Several days later, if Serenity has been defeated at least once, Dox will abduct Serenity to goad the player into another Shadow Game against him.
Until the player wins the Expert Cup, Dox will roam the first map at night and challenge the player to more Shadow Games.
When the player defeats Noah Kaiba and Gozaburo Kaiba, both Para and Dox are revealed to have been brainwashed by Noah. From this point onwards, they become friendly to the player and challenge him to normal duels in the first map.