The Dark Star Cluster (暗黒星団 Ankoku Seidan) is a intergalactic crime network formed by four evil aliens.
They were first seen performing a robbery in a warehouse on Earth. When Alien Valky Halky's Samekujira Jolly, a very valuable monster weapon came to Earth for its master, the team approached Xio and Jolly's owner, demanding it until Halky challenged them for a rugby match.
Three days later, during the tournament, the Dark Star Cluster scored 51 points in the first half by cheating with their powers until Isamu's fighting spirit turns the tables in the second round. Enraged when Isamu called them no side after the game ended, they enlarged and began on a rampaging spree. Ultraman X in Gomora Armor arrived and sent them to the sky with Gomora Oscillatory Wave.