Let's jump right into it:
"In a certain reign (whose can it have been?) someone of no very great rank, among all His Majesty's Consorts and Intimates, enjoyed exceptional favor" (1).
This immediately reminded me of the opening line for Don Quixote, another lengthy, historic tale. Just as Cervantes's claim that he can't remember quite where in La Mancha Don Quixote was from is brimming with irony, Genji's introduction strikes me as slightly ironic as well. It may not be immediately evident (unless you consider just how long the book is), but Genji is rife with details about ancient Japanese court lifestyle. Considering that, there must be some intentional humor in the narrator's claim that she can't quite remember whose reign it was.
Yet, at the same time, we must also consider the fact that this is a female author telling us about the behavior of an Emperor in somewhat unflattering terms. Periodically throughout the book the narrator will address the reader directly, making claims about how it would not be appropriate of someone of her rank to reveal too much about what happened between these more noble characters. This could simply be the first example of the narrator revealing her own rank and status relative to those she is speaking of.
I think it is also worth considering that, to the original audience of this book, it was painfully obvious who she was referring to. In that case, this slightly sarcastic "whose can it have been?" interjection is not quite so subtle or deferential at all. She may be treading somewhat softly, but only because she knows her audience doesn't need the truth to be stated explicitly, just as all the poetic allusions that follow would have been evident to them as well.
Or, perhaps I'm just reading too much into this, and the narrator is simply attempting to establish from the beginning that, while this work may seem to be real it is, in fact, a fiction. Her original audience may have immediately known who she was referring to, but by slipping this uncertainty in she is effectively telling them "Any similarities to persons living or dead is purely coincidental."
Either way, I think it's safe to say that I think this is a captivating introduction to the *Tale of Genji. *