Where best to change Euro to Yen?

I will be visiting Japan end of the month for 12 days from Malaysia. I have EURO left over from my Europe trip. So I plan to exchange that to YEN when I reached Japan. I won't need to exchange any at Narita since I also still have some YEN left from previous time. But I read that EURO is not a good currency to exchange in Japan? I guess I can exchange Malaysian Ringgit to YEN back home but prefer to finish off the EURO. Any feedback, please? Where best to exchange EURO to YEN? How about AUD to YEN? Would that be better than EURO?
What is the operating hours of the Post Office and the Currency Exchange Counters? Do they all charge commission?

The Post Office does not charge commission. Hours vary depending on the size of the post office. The exchange window often closes earlier than the other windows.

Hello,

Am I correct in understanding that if traveling from Europe, the best bet is to exchange EUROs in Japan at the Post Office?

Thanks and regards,

-elvisrule