Impact of spouse credit on inheritance calculation for immigrant in Japan

I'm bored out of my mind at work this week and wanted to brush up on my React frontend skills (non-existent but you gotta start somewhere), so I thought making a simple inheritance tax calculator would be nice.

I'm focusing on the most common case that crops up around here: a foreigner living in Japan (henceforth we will call them Luck Gaijin, or LG for short) receives an inheritance from abroad, the deceased nor any other inheritor has never set foot in Japan and none of the assets are in Japan.

So I do the usual steps:

1. Assets visible to Japan is only the part of the estate received by LG
2. We take the count of statutory heirs, whether LG is one of them is irrelevant, to calculate the deduction: 30M + 6M * number of statutory heirs
3. We subtract the deduction from the assets in 1. and calculate the taxes owed by each statutory heir based on the standard statutory distribution.
4. Taxes owed by LG is the sum of all taxes in 3.

So with a specific example of 100M¥ received by LG from their dad, with a surviving spouse and LG's sibling, we would have:

1. 100M¥ assets visible to Japan
2. 30M + 6M * 3 = 48M¥
3. 100M – 48M = 52M¥
   1. Spouse gets 50% but spouse gets a special deduction so no tax owed on 50% of the estate
   2. Each child gets 25% so that's 13M taxed at 15% with a deduction of 500k so 1,450,000¥ owed
4. LG owes 1,450,000 * 2 = 2.9M¥

That's my understanding now, but I have some doubts about the step in 3.1. with the spouse special deduction. There is mention in other threads by u/starkimpossibility that it works more like a tax credit than a deduction. So is it applicable in the scenario at hand?

If it is applicable, it gives a huge discount for our Lucky Gaijin.