Arthur

Arthur is an X-Tower knight bike rider. He first appeared in Gabu's tournament where he beats Taiga. Prior to his battle against Koei, he stumbled onto a plot by the Four Kings only for them to be thwarted by Koei. In Gabu's tournament, he lost to Koei due to interference by the Four Kings. His Idaten Bike is called Hammer Head.

[Spoiler] It is later revealed that he worked alongside Yuki to help protect the secrets of the X-Tower and heal the X-Zone. [/Spoiler]