I don't know. Before I was made aware of this, I tried tipping while in Japan. Several places people were very dismissive about it. Eventually I just stopped, because it seemed like people didn't want tips.
It's correct to say that in Japan one should not tip. It's not correct to say that it's considered offensive.
To seriously offend some Japanese people you'll have to do something crazy like stick your chopsticks straight up in your rice bowl. Then you'll see them really wince ;-)
To seriously offend some Japanese people you'll have to do something crazy like stick your chopsticks straight up in your rice bowl. Then you'll see them really wince ;-)