I didn't expect I'll have to address it, but yes, in case of tonkatsu the sauce would be most surely katsu sauce. What I did was - generalizing on the concept of "seasoning factions". My bad, I guess it didn't transfer well with my note. Was not doing it in context of tonkatsu, but in general. And I believe, if we look at Japan from the western pov, the first sauce that comes to mind will be soy sauce, shoyu. It was also mentioned in the source I came across while thinking about this note.Usually in the context of tonkatsu, sauce means katsu-sauce.
Your mileage may vary.
I'd better not comment on which sauces I use for what. But pls read my reply above. :')Pork cutlet with soy sauce?
Savages.