Erronius
Lanx
Is 100% correct on that yellow box Go Go Curry being amazing. I buy the identical brand here, but I get 60 single packs for $100. That amazon link is 20 x double packs for about the same, which isn't too bad considering it's imported goods. The packs are $5 in the stores and that is under that.
As for katsu, it's crazy easy to make. I personally prefer Chicken Katsu (You get both Chicken and Pork Katsu at Go Go Curry restaurants when you get the Major Curry which looks like this:
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and
Chicken Katsu (Video) チキンカツ link seems pretty reliable. You literally only need these ingredients:
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Your Katsudon should look like this:
View attachment 448769
The pork should have softly cooked egg all around it and there should be plenty of onions and a hint of sweet sauce.
Or you could just go to New York/Boston which has actual Go Go Curry shops.