Does the weight seem the same? Most counterfeits weigh less (sometimes much less) because they skimp on internal components.
Are there any visible defects or blemishes in the brick or the cable or connector? Does the plastic of the brick look & feel the same as the original?
Does the printing on the adapters look the same?
The older Apple chargers put the serial number on the charger like that, but more recent chargers put the serial number into the bottom of the opening where the AC Cord or Duckhead adapter connect.
The packaging looks like what Apple uses, but I've never seen a Japanese packaged one so I don't know. I know years ago (back in the PPC days) we had to purchase power adapters in bulk from a reputable third party vendor. While they looked identical even with the Apple logo on the brick and they even worked just fine, the barrel types were much harder to insert into the laptops to the point I thought we would break something (never occurred with a known genuine Apple charger). We used them because we had no choice since we could not purchase any directly from Apple at the time (I forget the reason Apple had run out of them).
The best way to know if you have a genuine Apple charger is by purchasing it from a known reputable vendor and authorized Apple reseller or directly from Apple.
