The Invisible Challenger is the sixth episode of Metal Cardbot, and the first appearance of Shadow X.

Plot

Jun has been experiencing a series of strange mishaps and pranks throughout the day. When he arrives at Edo‘s workshop, he discovers that the Metal Cardbots all had silly faces scribbled onto their faces while they were asleep. The culprit reveals himself as Shadow X, a stealthy VTOL Metal Cardbot capable of turning completely invisible. Shadow X taunts Jun, expressing disgust at the idea of becoming an underling to a human child wielding the Metal Breath, and challenges Jun to try and seal him.

Jun and Blue Cop chase after Shadow X to the docks, where Vera is filming a dance video with her friends. Shadow X engages stealth mode to attack Blue Cop while invisible, but Blue Cop tracks him via his shadow and lands a Megavolt Punch. Shadow X recovers and uses his Heli-Tornado to send Blue Cop flying into a nearby shipping container. All the while, Vera has been secretly capturing a video of their fight.

Victorious, Shadow X denounces Jun and his team, asking Blue Cop if his relationship to Jun is akin to an underling. Before Blue Cop can respond, Jun proclaims that Blue Cop is his friend. He reveals that he has a “secret weapon” specifically designed to counter the Heli-Tornado and challenges Shadow X to a rematch. Intrigued by the challenge and definitely not scared of the “secret weapon”, Shadow X flees, leaving Blue Cop and Teo to ask what Jun’s secret weapon could actually be.