Yen goes up, Nikkei goes down... because Japan is an exporting nation. More expensive Yen means less exports which hurts underlying economie.
The swing in de NKD, which is USD-denominated will be less in this case compared to the actual Nikkei... so the correlation will actually be less I assume.
Both futures are completely different though. NKD is equity index and 6J is forex... the only strategy I can think of is if you make assumptions on which level in Yen equals which level in the Nikkei... which is more a gamble then an actual strategy