I've flown JAL about ten times (and ANA about 40) and have never experienced overt discrimination. I may have had a Japanese passenger or two ask to be moved from my row to a row with more seats available, but I would have done the same thing. I may have had an FA or two that didn't like serving non-Japanese, but the FAs in question brought out Kirin upon request and were as attentive as any - because that was their job.

Overall, JL and NH are two of the best airlines I've ever flown on and take care of their passengers - even in Y. I've only flown NH a few times in J and all of my JL experience has been in Y. I'm usually on a budget and choose the Japanese carriers specifically because of their Y service. No complaints here.

FWIW, I speak enough Japanese for short conversations.

You want disdain for passengers, I could point out a few UA and NW FAs (though to be honest most of them aren't bad).

Seriously, I'll keep flying JL and NH when they fit my plans until they convince me not to. I'll be trying FCO-NRT-FCO on JL next month - perhaps I'll write a trip report.