Thanks for the tag @
juvela!
@
malcala622 - pictures in the ad aren't the best, so this is gonna be a semi-rough guess.
I think this is a 1986-ish
Nishiki Tri-A.
I'm not a Nishiki expert (so @
T-Mar, please chime in with any additional info or corrections) but I think 1985 Tri-As had semi-wrap seat stay caps and internal cable routing throughout. '86s (most of them, anyway) had top tube internal cable routing like the mystery frame and external routing everywhere else, with the chainstay cable stop slightly on the side of the tube (as opposed to directly under or on top). Mystery frame shows no grommets on the down tube and the right side chain stay isn't fully visible, but I would bet you'd see a side mounted cable stop.
By 1987 the top tube cable grommets were moved to the underside of the tube and the chain stay cable stop was attached on top. The brake bridge was also different.
So, a nice Tange 1 frame but nothing fancy. It looks like at least a partial respray (I can't decide if the seat stay caps were just painted over that "N" decal or if the decal came off and paint was applied right over the residue). The fork is probably original, too - that sort of rounded crown was used on Tri-As and Tri-A Equipes.
Here are some pics:
