If at any point in time the adventurers are fighting dragons in an eastern themed game, something has gone terribly wrong.
Why?
I am coming to the end of a 10-year Rolemaster campaign set (more-or-less) in Kara-Tur. The PCs have fought dragons on multiple occasions, as one aspect of their ongoing struggle with various factions among the Sea Lords and Storm Lords. One of the PCs is also involved in a romance with a dragon whom he met in the course of these adventures.
This ties into something else that bothered me-if one player has a samurai character, for example, can he really go off with the other party members, or is he stuck doing step-and-fetch quests for his master all the time?
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play around with the traditional tropes and use them to your advantage. Maybe that samurai isn't devoted to a master, but rather a philosophy inspired by real-life Bushido. The samurai seeks to live his life according to those principles, which grant him tremendous power and skill. At the same time, he acts as an adventurer to gain honor and fame for his clan, as well as treasure to increase its social standing.
In our game it didn't turn out to be that hard to get the samurai involved in adventuring.
First, they are the last survivors of their clan, which was on the losing side in a civil conflict. So they do not have lands to manage and do have honour and wealth to restore.
Second, they got sent on a mission by their daimyo (the head of another clan with whom their clan was allied). This mission ended up having them travel to various foreign parts where they successfully defeated enemies, attracted the attention of various players both in heaven and in hell, and gained 10+ levels (adapting various old AD&D modules such as OA 3, OA 5 and OA 7).
Third, their return to their ancestral lands coincided with their defeat of the ruler of Freeport (rebadged as a pirate town of the coast of Kozakura - I adapted the Freeport trilogy modules to be a mid-teens RM adventure). One of the samurai had himself installed as daimyo of that island. The PCs therefore have a base of operations and no immediate master from whom instructions have to be taken.
The game definitely has an Oriental Adventures feel - there are samurai wielding katanas, a warrior monk wielding a tetsubo, an esoteric "mind monk", a fox spirit ranger/ninja, a tree spirit "druid", etc. Fighting styles used by the PCs inlcude Light Sparkling Water (name taken from the Kara-Tur books), Jasuga Slice, Jade Harvest, Heavenly Pagoda, Diving Phoenix, Port in a Storm, and Tolling Bell of the Western Paradise (named by the players - the last is the style used by the tetsubo-wielding monk).
The main plot lines of the campaign have revolved around conflicts between various factions among the gods, the lords of karma, a number of more-or-less powerful nature spirits, a handful of petty demon kings, and various "super-enlightened" (Cthulhu-esque voidal) beings who are located off the wheel of karma and threaten to disrupt it. In some ways this could be like any planar-travel-heavy D&D game, but rebadging things and tinkering with them a bit to link them into the celestial bureaucracy and the lords of karma goes a long way to changing the flavour of the game.
Secondary plot themes have involved various earthly conflicts between families and factions. As someone posted upthread, this also seems to work as an OA-trope.
Rolemaster has fairly robust rules for unarmed, unarmoured martial arts, but these haven't played all that big a role in the game. Since one of our players moved to England a couple of years into the campaign, the warriors have all been weapon users. Issues of social class and status crop up from time to time. The ninja's main solution is to cast a Disguise Self spell (Facade, for those who know the Rolemaster terminology) to appear as a samurai. Most of the PCs have fairly well developed social skills, but I think this is pretty typical for Rolemaster characters (because facilitated fairly well by the system's character build rules) whatever the gameworld.
Overall, I think that what is important is not historical or cultural detail (which, as others have pointed out, tends to be ignored in most European-flavoured D&D-type fantasy) but rather a few key tropes - katanas, nature spirits, warring clans, lords of karma, rice instead of wheat, etc - that resonate with the players and make them identify the gameworld as being asian-themed.