Sweet Jiminy Christmas! That's a *very* nice old Nishiki! Are those black Dura-Ace high-flange hubs? Oh, geez, and it's orange, too...
I think you can push the rear freewheel to a 14-30, but that's about it. If you had a
long-cage Suntour V GT Luxe, you could go to a 14-34, but that's about it without a crankset change. The smallest chainring that will fit on that set is 42 teeth.
You could put a triple crank on it and get really low gears without changing anything else, but most of the currently available cranksets would stand out like the Dalai Lama at an Elvis convention. Velo Orange offers a
nicely-styled triple crank that should work on that bike:
Please post this picture over on the Classic & Vintage forum. It's definitely both.