Buying wine in Japan when one is from and returning to somewhere that actually makes decent wine is silly I am afraid. Import costs associated with taxes and transport make any wine here pricier than Germany, London, or Canada. Plus buying wine there offers a far better selection. A $20 wine in Europe can be quite stellar. Here is is likely to be garbage. If you are looking for Japanese wine a better thing to do would be ordering it online for delivery at your hotel in advance of your arrival.
Their domestic, non duty free French champagne prices often beats prices from the LCBO in Ontario (taxes in too). same with US MSRP prices. And they're way better than Korean prices.