This frame encoding has its origins in
Danish bicycle VIN system.
The W stands for “other manufacturers”. HJ for 2013/2014.
At that time, the Nishiki brand was owned by a Scandinavian company.
This company only had the name Nishiki in common with the original Nishiki bicycles from Kobe/Japan. nothing else .
https://en.wikipedia.org/wiki/Danish_bicycle_VIN-system