User blog comment:Gundam Legilis/Post clip highlights - Pyrrha vs Mercury/@comment-25091485-20140624011644

One thing to note: Mercury kicks to his left for the majority of the time, whether he is doing roundhouse kicks or otherwise.

This probably because Pyrrha's shield hand is to mercury's right and kicking to the left would make it much harder for Pyrrha to block. Case in point, the last part of the clip, if he had kicked right instead, Pyrrha would have easily blocked with her shield and countered.

Also its worth noting that Mercury parries Pyrrha's strikes with his ankle gauntlets multiple times in the clip :)