Are there are T-Bill equivalents or ETFs one can buy from Japan?

[TokyoBoglehead]

A Simple rule of thumb is, if you don't have bond/annuity style investments, stay at least 10% cash. Once you hit 1milion yen per dependant I think pursuing OPs suggestion is valid.

However, trusts are king here over ETFs.

Moving house and switching jobs can easily cost 1-2 million yen (or require the capital when you await your first paycheck).

So a few million is not crazy family, rather it's standard of you have the means.