He's using the Ahtal-Ka Great Sword, if that's your question. All of Ahtal-Ka's melee weapons are pretty ludicrous - their final upgrade gives them 330 Attack, a decent amount of purple sharpness, 0% affinity and THREE decoration slots, making them super-versatile. For weapons that deal lots of hits like the Dual Blades, you _need_ Sharpness+2 and/or Razor Sharp to make them viable, as once you burn through that purple, it goes through its white, blue and green sharpness VERY quickly. But since the Great Sword specializes in dealing single big blows, its small amount of purple isn't an issue, especially with Challenge Sharpen (which randomly restores Sharpness upon sheathing your weapon when facing an enraged monster) and the sheathing involved in using Valor style.
I’m a hammer main. I found the Ka weapons to be pretty good in that regard as well, however if I choose to go adept or aerial, the seregios hammer is great to maintain sharpness.