Question about my understanding on gift tax and some cryptocurrency stuff

I'm a regular poster here, but I made a throwaway cause I don't want this post linked to my main post. Mods, I hope this is okay.

I spent a few hours last night looking around on tax implications/regulations for gifts and cryptocurrency gains in general, and there's one thing that I'm still confused about that I'd like to figure out.

So here's the thing, I have some bitcoin (not too much) that I bought years ago before moving into the country. I'd like to minimise taxes I pay on them if I ever decide to sell them. I noticed a post from years ago by /u/starkimpossibility mention that any bitcoin/crypto transaction that is within your own wallets does not count as a taxable event (as long as you don't exchange one currency for another). Also, if you send the bitcoin to someone else as a present, they fall within gift tax for the receiver rather than counting as a taxable event for you. As long as you stay below the yearly 1.1mil JPY threshold for gift tax, you (as a receiver) don't have to pay tax on them upon receipt.

So here's my questions:

1) Assume I send 1mil JPY worth of BTC to my girlfriend, she now sells them for 1mil JPY. The assumption is that the exchange of those BTC will not incur into any tax because the price at time of "purchase" (= receipt of the gift) is the same as the price they are sold at (give or take some possible fluctuations). So now she has fiat currency of 1mil JPY that got transferred without triggering any tax.

2) What if, after sending said BTC, I decide to buy an equal amount (1mil JPY) of BTC with my own savings. I assume profit from these BTC at the time of sale will be calculated based on the time I bought them (as "new" BTC) rather than be calculated from the average with the BTC I used to own (the ones I gifted out). Is this correct? Is this a viable way to "reset" the average starting point from my crypto holdings?

3) What counts as a gift? What if my girlfriend also has 1mil JPY worth of BTC (or less, I don't know) and she decides to also gift me her BTC like I did with her. Do we both get 1mil JPY tax-free? Taking out the crypto from the equation, what if I give her a 1mil JPY cash gift and she gives me a 1mil JPY cash gift. Are these counted as gifts or is there something trickier going on here?

4) Based on question 3, what if I gift her 1mil JPY via BTC, then the next tax year she gifts me 1mil JPY (cash).

5) Now, imagine my girlfriend is actually my wife. Are gifts possible between spouses (under the same 住民票) or are they not considered as gifts, assuming we keep our finances separate?

I tried looking up all these questions and I couldn't get a clear answer on them. I know taking financial advise from Reddit is not a good idea and I'll probably consult with an accountant for this, but I'd like to do some research myself beforehand too, and this post is some of it.