As did I, in those little glass jars with non-airtight caps which necessitated the contents staying upright. It should have been obvious to get the foil sealed cups except I'm a huge sucker for tiny glass jars. I should also mention that I've seen these locally at Korean bakery chains like Paris Baguette in USA. It doesn't taste as good as those made in Hokkaido but possibly a way to try it without having to schlep it 18+ hours. Or in my case, chilled takkyu-bin from Hokkaido to Tokyo, a few days in the hotel fridge as the sticker sealed box was too big for the mini (and probably not cold enough), then a TPAC.

Freshly made daifuku survives as a carry-on, box(es) sealed in ziplock. Just avoid the ones wrapped with leaves or containing fresh fruit/cream.