I was interested too so started googling.

It was probably a comment by mikekchar: https://news.ycombinator.com/user?id=mikekchar

According to this response by CaptainZapp (the GP) on one of his comments ( https://news.ycombinator.com/item?id=17004877 ):

  Hi Mike,
  About six month ago you helped me through the "minefield" of eating as a gajin in Japan.
  Let's call it a rousing success (it helps if you even like natto, but I digress).
  Let me state for the record that your posts are shear awesomeness in contents and the amount of information provided.
  Thanks!"

I couldn't find the original comment by "mikekchar", but when you google "site:news.ycombinator.com mikekchar japan" you find many interesting comments about Japan.

It took a bit of digging (and a look into my passport to get a hang on the time line, but here we go:

https://news.ycombinator.com/item?id=15148389

Edited to add:

A reply to Mike's comment reads as follows:

"I just wanted to reiterate how amazing your comments have been here. I honestly feel it's a disservice to you to have your words languish in soon-to-be-forgotten HN threads. I'd love to read a blog of yours, or something along those lines!"

I very much agree. It's hard to describe my appreciation for the time he took out to write it. And it was more than helpful. If you're in Japan and only slightly adventurous when it comes to food those paragraphs include everything, which you need to know about the subject:

Thanks Mike!

Thanks to eneveu's googling a copy of the comment by the original GP is here :)

https://news.ycombinator.com/item?id=17046753