Inheritance tax on a Japanese national receiving an inheritance from an unrelated foreign national+resident

Scenario:

• I am a US citizen and resident. I have never resided in Japan (my domicile/住所 has never been there). I have no "statutory heirs" (in the Japanese sense) who have ever resided in or been citizens of Japan.
• My friend is a US citizen (born on US soil) and Japan resident (PR). His wife is a Japanese citizen and Japan resident. They have a child, who is presumably a dual-national until/unless the child decides to renounce one citizenship.

I would like to set aside some money (equivalent of less than 1 million JPY each year) as a future gift to my friend's child (for college tuition, a first home, etc).

The understanding I've come to is that:

• Directly gifting the money to the child will probably not incur Japan gift taxation (since it's below the 1.1M JPY limit; but gift taxes could be incurred if the child has received other gifts in the same tax year), but the child will incur capital gains taxes each year (if the gift is invested in a dividend-producing asset), and this will force my friend to file a tax return on behalf of his child when he would otherwise not have to.
• Putting the money in a UGMA/UTMA account in the US, in which the child has the legal right to the money when they reach the appropriate age, will be viewed by the NTA as a gift to the child in the year when I make the contribution. The child will subsequently have capital gains tax obligations in Japan, same as if I had directly gifted the money and my friend invested it on the child's behalf.
• Putting the money in a 529 account with the child as the beneficiary has the caveat that money distributed from the account to the vast majority of Japanese higher educational institutions will be non-qualified (since those institutions are ineligible for US federal student aid), and hence will incur penalties with the IRS.

The first two (direct gift; UGMA) seem like a hassle for my friend, and the third (529) doesn't seem advantageous. So I'm considering doing this instead:

• Put the money in a US taxable brokerage account that is 100% under my control and pinky-promise my friend that I will liquidate the account, pay US capital gains taxes from the proceeds, and transfer the remaining money to the child whenever the child requests it. This may incur gift tax obligations in Japan for the child when they receive the money (say, at age 18), and also incurs US gift reporting obligations for me (since the value of the asset probably will exceed the yearly exemption) but no US gift taxes for me (since I'm not going to be anywhere near the lifetime exemption). However, if the gift is for the purpose of living/educational expenses in Japan, the gift may be non-taxable in Japan.

I hope I've gotten everything right so far.

Now, the question I have is: what happens if I die before the child requests the money? I intend to write my will such that the brokerage account (or the value of the assets therein) is willed to the child in the event of my death. I'll incur no US estate tax obligations (I'll be below the federal exemption and I live in a state with no state estate tax), but I am having trouble figuring out how Japan's inheritance tax will apply when the child receives their share of my estate.