Can Bitcoin or other cryptocurrency count as assets for the naturalization fiscal requirements?

One of the requirements for naturalizing is to show you have a reasonable chance of supporting yourself financially until the end of your days without ending up in poverty or on welfare in Japan.

Being wealthy or even well off is by no means a requirement. Being stable and predictable and consistent, however, may be. Also, you do not need to be self-made or self-sufficient; you may include assets and revenue from your family and household if you can show they are a consistent and reliable source for your livelihood.

To prove this, you will be required to complete a two part form known as the 生計の概要 {seikei no gaiyō} (Livelihood Overview). The form is divided into seven sections:

1. income
2. expenses
3. main debt
4. real estate
5. savings
6. stocks & bonds
7. valuable property

One of the requirements for assessing livelihood in Japan is that you have a relatively stable source of resources that is evaluated or translates to Japanese yen. Obviously, no cryptocurrencies are denominated in Japanese yen, and their value is not considered even remotely "stable" as even compared to stocks (nor are there government regulations to protect or control these assets), so their value can fluctuate extremely wildly and unpredictably at any time.

Thus, if an applicant plans to emphasize that they plan on living in Japan based on things other than "income" and "savings", they'll need to pre-convert a certain portion of their assets to a form that can be converted quickly into Japanese yen and the conversion ratio is relatively stable.

As part of the proving of livelihood form application, you'll need to provide proof via paperwork such as bank account statements that show not only your current balance, but the history of your balance (to prevent scams such as temporarily borrowing a large sum of money to boost the balance, show the statement, then quickly returning the money).