The four kings are a part of team ST. They follow Gabu everywhere and listen to his commands all the time. They all have MTBs that look the same, dark green. They feel very jealous of Koei the ninja rider and want him to think that hw needs their help to win the idaten battles with Arthur and Sho.
All of them are like frightened little kittens who keep tagging behind Gabu. They are very close friends with each other. They feel confident when near Gabu but are very scared of him. They don't like idaten battles and are very loyal with anyone who is friendly with them.
The four kings were in team shark tooth all along from the real world to x zone. In x zone they share a place with Gabu as the rulers of x city. During the idatem battle tournament, while Koei was racing with Arthur, they put a bomb in a building and blasted it over Arthur. Thus, Koei won the race but did not appreciate it at all. During the race between Sho and Koei also, they took advantage of Koei's smoke bomb and attacked Sho in the middle of the race. Later, when Gabu leaves them and rushes off in his own direction, Sho saves the four kings from the people in control of the dark emblem. They then decide to join Sho in battling with team X.