Is Lightspeed Flash faster than light? I'm wondering if Lightspeed Flash has the power to travel at the speed of light, or is faster than it, or is it just some kind of hero name?
Flashy Flash hasn't shown any of his abilities or powers in the manga or at the tv show. But in the webcomic series of ONE (the original manga), which it has a lot more chapters, we know some of his abilities and his powers.

SPOILERS

So according to the webcomic:


   One of his moves, was to fly to the enemy within milliseconds and attack him from any distance. Flashy Fist (閃光挙, Senkōken): In only a matter of milliseconds, Flash traverses the distance between himself and the opponent and unleashes a barrage of punches. 


So you have to wait until to the point where the manga, will show more about this character.