It seems as though Square Enix’s well-received Octopath Traveler on the Nintendo Switch has performed well as the game is currently experiencing shortages in Japan. And yeah that is fast.
No actual numbers have been made available but Square Enix has taken to Twitter to apologise to those wishing to purchase a physical copy of the game and they suggest purchasing it digitally or getting a Nintendo Switch download card at their local shop while the issue is sorted out;
3連休で一部品切れのお店が出ているようで申し訳ございません!
DL版や、ローソンさんで販売中のダウンロードカードもご検討いただければと思います!#オクトパストラベラー— オクトパストラベラー公式 (@OCTOPATH_PR) July 14, 2018
Of course if you are not fluent in the above it does not translate that well but you get the gist; bad news which actually in itself is good news.
Have you looked into Octopath Traveler already?