[Nyororin]

Nope - You CANNOT get Reese's Peanut Butter Cups here.
Seriously. I have hunted for them all over, and the ONLY option for buying them was a place on Rakuten that was selling a single pack for 800+ yen. I am sure if you scour every tiny little specialty shop you could find them somewhere, but I have yet to.

They are one of the very very few chocolate type snacks that has neither a Japanese version nor an importer. They are not even in the order books for wholesale importers. Costco doesn`t even carry them.

Costco does occasionally have individual serving Reese's Pieces included in their big box-o-snacks.

...
If you can`t tell, I really really like Reese's Peanut Butter Cups...

And I haven`t had one in 6 years, since I was in the US last for a visit. And I have been hunting for them ever since. One of the very few US chocolates that is not sickeningly sweet...

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Also - another foodstuff that you simply cannot find in Japan; Eggnog or Eggnog mix (the liquid stuff you mix with milk). I have been hunting for a week for some... (I refuse to order from FBC, they overcharged me, then said I never paid them and charged my credit card repeatedly until I changed the number.)