For the samuri example. it's worth noting that the Rokugan d20 system specifically allowed players to play samuri fighters (basic samuri) samuri spellcasters (Shugenja) samuri rogues (Scorpion spies as well as the courtier class) samuri barbarians (Crab bruisers who, while embarassing, are valuable on the wall) and samuri monks (Samuri who have taken monk vows). So themes may be a lot more flexible than you might think.