Zatoichi, Lone Wolf and Cub, Yagyu Conspiracy, and many other films and TV in the jidaigeki/chanbara genre remain favorites and continue to inspire my games.
Give them a try.
To add bit more of this cinematic flavor I've added two new additions for my own OSR OA games. These are primarily aimed at my own versions (classes soon!) and two of my favorites Ruins & Ronin and Shinobi & Samurai. The additions can be used with any other OSR D&D games, not just the Oriental flavor, although I feel they fit best for this genre given the quick strike and deadliness of the one on one samurai duels in these films
Note: The Duel addition is supremely lethal for characters, especially low to mid level characters. That's the nature of the game. Young or inexperienced characters will get wiped out quickly in a duel. Duels should be a rare and lethal thing of beauty between characters of close level or fighting skill. A duel between higher level masters should be a thing of awe and majesty. Use sparingly. The foolish will get themselves killed quickly.
Assessing Another's Fighting Skills
An observer can watch another and evaluate his to hit roll and bonuses for attributes and class abilities.
To do so the observer must watch his subject intensely for a number of rounds based on the observer's level.
The Assessment Roll
After watching his subject the observer can roll 1d6 and attempt to roll under a target number based on the oberver's base to hit bonus + his Intelligence OR Wisdom bonus/penalty (choose the most advantageous.)
IF the subject is not fighting this number is halved (round down.)
Example: Watching a swordsman practicing, a fifth level Bujin (+3 BtH) in R&R with an Intelligence of 15 (+1) would need to roll a 4 or less on 1d6 after three intent rounds of study to gain information on the swordsman's skills.
If the swordsman was not duelling, just walking in the street for example, the roll would be halved to a 2 or less.
If successful on either roll the observer can learn the subject's base to hit, the bonuses or penalties to the attribute modifing the attack roll, and any class bonuses with the weapon in use.
If unsuccessful the observer must wait until the subject can be observed fighting to reassess.
Hiding One's Skill
The subject can attempt to hide his true skill from potential observers. While fighting he can adjust his total to hit bonuses from his level, attributes, and class abilities down to +0. If successfully observed the false reading would be gained instead of his true ability.
It is more difficult to hide one's true skill when not fighting. Suppressing one's movements and reactions from dedicated training requires the subject to make a Saving Throw to adjust his total to hit as above.
Duels of honor are very serious affairs. The potential for quick damage and death to both combatants is high as they line up face to face and come right at each other. It is a collision of steel and bone as warriors prove their bravery and skill. The longer the warrior's face off the more damage they can deliver and receive as they mentally shift and adjust, potentially leaving themselves open to damage as they try to outthink and maneuver their enemy. It is not defensive fighting, this is not war combat, this is not trying to inflict damage on the enemy while doing everything possible to keep from getting hurt. This is a lethal risk vs reward combat as they remove regard for own bodies and live to prove their worth and superiority. To save face and honor.
The Duel is composed of two phases: The Staredown and the First Strike. If a third party interferes with any part of this process the duel is unresolved and normal combat resumes immediately.
Once damage is resolved, and both combatants are still on their feet and able to fight, they may begin another Staredown or continue with normal combat.
The two combatants face off one-on-one, take their stances, and begin to silently study and make mental and small physical adjustments to their opponent, preparing for the most advantageous attack, the First Strike.
The combatants can take up to five rounds facing off; each round taken multiplies the potential damage of successful First Strikes. They may take as long as they like but the damage adjustment tops out at the fifth round.
This damage multiplier is applied to BOTH combatants if successfully hit during the First Strike. However, damaged can be reduced for the combatant who successfully hits and rolls a higher total than his foe.
The First Strike
When one combatant decides to attack the First Strike occurs. There is no initiative roll, the attacks are simultaneous.
A normal attack roll is rolled. If both combatants have weapons in hand there is no penalty to the attack. If a Fast Draw rule is used, as I do in my games, DM's will use their own system to resolve this.
For my own games those without the Fast Draw ability suffer a -4 to their attack for pulling and using a weapon in the same round.
IF both miss their attack nobody takes damage. If only one combatant hits he takes no damage and his foe takes the full amount of multiplied damage from the Staredown. If both combatants hit, both take damage but the combatant who rolled a higher total than his foe will usually take less of a damage multiplier than his foe.
Two swordsmen, both using swords with a +1 adjustment due to high Strength (1d8+1 damage) attack each other after a Staredown of five rounds (x6 damage). They both hit: the first rolls a total of 11 the second rolls a total of 18. The second swordsman beats his foe's roll by 7, reducing his received damage by -4x.
The first swordsman takes the full Staredown damage adjustment of x6 damage receiving 1d8+1 x6 in damage.
The second swordsman takes only an adjustment of x2 damage receiving 1d8+1 x6 in damge.
Again, if both combatants are still on their feet they may initiate another Staredown or attack each other with normal combat procedures.