Inheritance Tax Question When Inheritance is Split Between a Japan Resident and Non-Japan Residence

I am an American. America does not have a federal inheritance tax, so this concept is new to me. Therefore, before anybody dies and before I receive any inheritance, I would like to understand how this works.

I understand the inheritance tax exception in Japan is 30 million yen + 6 million x each heir. I also know there is a progressive tax bracket for the amount of inheritance gained.

What I would like to understand better is if inheritance tax is based on the portion I receive, or the total sum of the estate of the decease.

I will give a hypothetical scenario.

Somebody dies. Combining cash, investment, and home, they are worth 300 million yen. The entire estate gets split three ways, between me and two other people. The deceased person did not live in Japan and the two other heirs do not live in Japan. Only I do.

I am on spouse visa in Japan.

Will Japan tax only my portion, the total estate, or 1/3 of the total estate minus the exemption? Or something totally else?

Calculations below:

100 million – 48 million = 52 million taxed

300 million – 48 million = 252 million taxed

300 million – 48 million = 252 million, followed by 252 million / 3 heirs = 84 million taxed

or something else?

EDIT: Thank you everybody! This has been very helpful. I am also curious about the repercussions of inheriting stock and real estate. How does the exemption work with those? Is it based on value of the stock or real estate? (I.e. If a house worth 20 million yen, does that mean that it’s not considered taxable, since it’s under the 30 million threshold?)

Also, let's assume I receive an inheritance in the form of stock market investments (individual stocks, mutual funds, ETFs, etc).

Hypothetical situation:

I inherit X amount of investments with the cost basis of 25 million yen. The value of the investments have increased, but have not been sold and are therefore the gains are unrealized. The unrealized gains have the stocks valued at 50 million yen (2 million yen above my example exemption if there are three total statutory heirs).

Does Japan see the value of my inheritance as 25 million yen or 50 million yen? Meaning, am I below the threshold with 25 million yen or above the threshold by 2 million yen, even though the gains are unrealized?