I don't think so; a quick Google search turns up nothing. L5R borrows VERY loosely from the history and myths of many different Asian cultures, so while Rokugan is certainly influenced by Japan, only the basic stuff (samurai and courtiers and such) is really drawn directly from it. Just about everything else is either an amalgamation of various ideas from various Asian cultures, or else it comes entirely from the writers' imagination.
This is even more true for modern L5R; while the original storylines may have been more Japanese-influenced, the subsequent ones became more and more Rokugani and less Japanese as the writers fleshed the world out more and more.
The common tie is probably just that a "city shrouded in mist" sounds foreign and exotic, so both the L5R people and the EQ people used the trope.
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