There are three video game sales trackers in Japan: Media Create, Famitsu and Dengeki.
Unfortunately, Media Create recently stopped publishing sales data publicly. So that leaves Famitsu and Dengeki.
For the sales in Week 17 (April 22-28) of 2019, this is the following sales data from Dengeki which is a Top 50 ranking:
https://dengekionline.com/articles/460/Rank: 38
Console: Switch
Game: 海腹川背 Fresh!
Publisher: サクセス
Release date: 19/04/25
Sales for this week: 1,231 units
Life to Date sales: 1,231 units
Famitsu publishes a Top 30 ranking weekly but Umihara Kawase Fresh! didn't sell enough to get in the Top 30.
The reason for referencing multiple trackers is to compare sales since they do have different methodologies.
Now, regarding Umihara Kawase Fresh! I actually expected at least 5,000 units sold for the first week before it released. So, 1,231 units is really bad even though I know this is a niche game series.
If you don't understand how bad that is, it is one of the lowest debuts for a software title in Japan this year and I follow game sales data regularly. The week 18 sales data also just released and it shows that Umihara Kawase Fresh! is not going to have strong continued sales weekly because it didn't chart in the top 50:
https://dengekionline.com/articles/592/_____
Here are comparisons from past games in Japan if you didn't know.
These are sourced from the following site which archives Famitsu sales data:
https://sites.google.com/site/gamedatalibrary/game-search

Note: The site is using the US localised name for Sayonara Umihara Kawase but this is sales data from Japan.
FW = First Week
LTD = Life to Date
You will not find sales data for the Super Famicom version of Umihara Kawase because it didn't chart in the Top 30 of Weekly Famitsu back in 1994. Even if it did, the magazine used a point system so you wouldn't get exact sales unit numbers.