Erza. AS is inconceivably faster but has no notable feats outside of speed (nothing impressive in DC and durability). And his feat of blitzing Haragiri only applies to his attack speed, not his reactions or movement.. so Erza would tag him eventually whether it be due to ranged attacks or greater stamina, while he has nothing that can break her more durable Requip armors. Samurai doesn't have any good piercing durability either; his best feat all around is probably tanking a punch from Monster Garou.
I suggest you to use the first chapter where Erza was shown and nerf her to the point the awful carbon copy series knows as One Punch Man can at least make a step without ending eradicated from the face of the universe by Erzas casualty dominance pressure.