Resetting Cost Basis as a Non Permanent Tax Resident

I have assets that are based in Canada that have appreciated significantly over the past 3 years. I moved to Japan in April 2022, and plan to continue living here indefinitely, so I will become a permanent tax resident at some point. I would like to reset the cost basis of my assets before that happens, which seems like it's allowed in Japanese tax law. There's a couple points I'm confused about, so I thought I'd ask the community here.

First things first, an NPR is a foreigner who has been living in Japan for less than 6 out of the last 10 years. An NPR becomes a Permanent Tax Resident if they live in Japan for more than 5 out of the last 10 years.

How are these 5 years counted? Is it 5 years to date? (if you moved to Japan on December 25th 2020, then you're an NPR until December 25th 2025)

Or is it counted by calendar years? (on your 5th year in Japan you're a Permanent Tax Resident starting January 1st)

Second, some kinds of capital gains by NPRs are treated as foreign income, and thus are not taxed by Japan. My understanding is that if:

• the securities are listed securities
• the securities are sold via an overseas brokerage
• the securities were purchased prior to the seller becoming a Japanese tax resident (i.e.: moving to japan)

Then any capital gains incurred from a sale are counted as foreign income, and Japan doesn't tax them as long as the money isn't remitted to Japan. Is this understanding correct?

Third, I'm curious about the interaction between the above two clauses. Let's say a person becomes a Permanent Tax Resident in June 2027, and in March 2027 they sell all of their foreign based assets (that meet the above definition) and immediately repurchase them (effectively resetting their cost base), and then this person does not remit any money to Japan in that year. Is this transaction taxed as an NPR? Or does Japan tax it as if they had been a Permanent Tax Resident the whole year?

Lastly, I'm confused about the reporting responsibilities of an NPR. As an NPR, do I have to report any incurred capital gains even if I won't be taxed on them? Do I have to report my foreign assets? Does this change after becoming a Permanent Tax Resident?

I didn't think I had to do that, so I've just been letting my company file my taxes for me the past 3 years. Do I need to amend my tax returns for the past 3 years? I've sold a couple assets each year to pay for management fees.

I'd appreciate any help!