Duels: Equipment and charms
Remember that you can change armor and charms during a fight, even if it's a duel.
We strongly recommend the Samurai Clan Armor, unlocked with the first step of Lady Masako's Tale. This armor is by far the best in the game in terms of defense: it reduces damage taken, increases life and gives you resolve when you take damage. Armor with offensive bonuses is also an option if you are confident.
When it comes to charms, anything that offers useful bonuses in combat is good to take, whether it's melee damage, damage reduction, healing bonuses, and so on. The Mizu-no-kami charm can be useful, as it allows you to parry, perfect parry and perfect dodge more easily. You can find it in the Spring Falls Shrine, north of Act 1.