Personally, I believe this is the hardest level in the game. It just takes lots of awareness. When one swordsman is defeated, the other will gain a new attack chain that does more damage than any other, and it hard to evade. The blue swordsman has twice as much HP as the red, so you want to take him down first. There’s no real trick; just stay aware, block everything and counter. They will parry you if you go super-offensive, so take it easy. All of their attacks have obvious tells, so just stay aware!
Once the blue swordsman is dead you must play cautiously. Instead of the areal spinning attack, he will dash and do a chop. It does a LOT of damage, and is staggered so if you block his previous attacks you cannot block it. Your best bet is to “bait” him into attacking by charging him, then rolling away. Once you see what attack chain he uses, counter with your own. If you get lucky you can bait a low sweep and chi-counter him for 1/3rd his health. Swordsmen are susceptible to being juggled.