Koei

A ninja biker hired by Gabu. He first appeared to take on Sho and Kyoichi. He injured Kyoichi, broke his MTB Thunder Emperor, and took out the Four Kings that were battling Makoto. When he battled Sho, it ended up a draw when the Four Kings interfered. He thwarted another plot by the Four Kings when they tried to "assist" him when he thought of it as dishonorable. In his battle against Arthur, the Four Kings successfully interfered causing Arthur to lose. It is later revealed that Koei works for Gabu because he couldn't afford a doctor for his sister Kiku. Once she was rescued from Gabu's clutches, Sho and Koei battled again and he lost. Afterwards, he stopped serving Gabu and aided Sho in defeating him as he took out the adult members of Team ST. Later, he ends up under the control of Team X and was freed by Sho. He has Taiga watch over X-City while he is away.
His Idaten Bike is called Aero Scissors.