I talk about the moment when Zoro used Asura on Kaido.
If you look at the image below where Zoro prepares his attack, you can see Kaido swinging his club to attack Zoro, but for some reason he shouts “UGH!!!” and you can see those white sparks around Zoro.
They are the same sparks that were used when Zoro destroyed all Hyozou’s swords and usually used when someone is blocking attacks.
キン stands for metallic-sounding
So an half dead Zoro with a little of strength and broken bones was able to block Hybrid Kaido’s attacks (three times) and afterwards to speedblitz him causing a permanent scar.