Perhaps the single most apparent indicator of a new release's popularity is how hard it is to find a copy on the shelf of your local retail stores.
Sure, there are factors like how many units got shipped to a given region based on research, but overall, if you can't find a new game on the shelf, it's likely selling far better than expected. A tweet from the PlayStation Japan account seems to indicate that's the case for Ghost of Tsushima.
『Ghost of Tsushima』は、おかげさまで予想を上回るご好評をいただき、一部の店舗で品薄となっております。
— プレイステーション公式 (@PlayStation_jp) July 22, 2020
The tweet states that the game has received a far better reception than anticipated and that some stores have run out of stock. They also have indicated that new copies are being produced, and the digital download version is available on PlayStation Store.
While official sales numbers have not yet been released, and certainly not with any regional breakdowns, Ghost of Tsushima seems to have become a critical darling among the Japanese gaming press. Game magazine Famitsu gave it a perfect score of 40 out of 40 points, only the third game out of a Western developer to achieve that feat alongside The Elder Scrolls: Skyrim and Grand Theft Auto V.
Until those sales numbers are released, or at least mentioned in the next quarterly report for Sony, we can only speculate based on the available information. But if Sony is telling customers stores are running out of stock, it suggests either a short initial production run (on the assumption that Japanese audiences wouldn't be interested in a samurai game out of an American studio) or a typical production run which failed to account for an unexpectedly enthusiastic reception from the press and consumers.
Either way, Japanese gamers are going to have to wait or shell out on the PlayStation Store. Our own Game Luster review of the game is in progress.