JR Duty Free also provide 20% off for online purchases.
I know a few years back one of the companies who got booted out of Wellington airport started offering this for pickups only (they had no physical store at the airport). They could offer 20% off because the airport didn’t take a cut of the sale as it wasn’t in their physical store.. It makes you realise how airports make money apart from parking!
There are actually lots of things in duty free that are now more expensive than buying retail. You’ll find plenty champagne is cheaper at a supermarket even when it’s not on special. I also looked at a few whisky’s recently that were cheaper retail than duty free. The 20% off however did bring them down below the retail store.