Best advice for duels is not to get too caught up in trying to be clever. Hardest duel for me was in the Mythic tale 'Way of the Flame', just because you have to manage the elemental. But basically three things on duels worked for me on hard.
1. Spacing - only use counter attacks, expect to die the first few times as you get familiar with their patterns. no point spending resolve to revive etc. Then just stay a couple of steps back, out of range. This way you can avoid the unblockables much easier with a sidestep and the dodge gets you out of range of lunges. Also pay attention to the circular arena, If you reach the edge the distance will close and you'll get trapped. Ronin generally sheath swords before an unblockable.
2. Perfect Dodge - Probably 2/3 of these on normal attacks, give you one time damage chunks
3. Perfect Parry - As above, can probably get 1/2 of these depending on confidence (wear a charm that makes the window bigger)
4. Blue attacks - Forget what these are called but a normal block turns them around for three quick swipes
5. Resolve - You'll need to heal obviously, but wear armour, charms that generate resolve quickly as well. Only use the triangle/circle combo when they are staggered, and use the L1 + R1 dance when they have a third of their health left