Looks like an old Nishiki ONP frame from the mid-late 1970's.
These were a special high-end model Nishiki offered, similiar to the Schwinn Paramount program - i.e. a limited production high-end frame model that had almost nothing in common with the rest of Nishiki's lower-priced massed-produced bikes. A product intended to demonstrate the company's engineering and design knowledge and capabilities better than the $149 - $249 typical product they were perhaps better known for.
Not that there is anything wrong with mass-produced low-priced bikes . . .
The bb shell cut-out is the give-away clue, along with the fastback seatstays. I believe they originally were only available in a "Champagne" gold color.
I wanted one, never got it.
Regards,
Mike Fabian
San Francisco, CA