Kirk here with some notes about my quarantine experience. Main point: Being far away from Japan's biggest hub airports makes international travel significantly harder for those of us in Kumamoto.
Secondary point: The app we must use (MySOS) doesn't seem to take the need to travel back to Kumamoto by car into account.

First of all, the rules:

"From January 8,2021, all those who enter, re-enter or return to Japan (including Japanese nationals) are also subject to conducting of COVID-19 test upon arrival no matter whether arriving from the countries/regions designated as an area subject to denial of permission to enter Japan or not until further notice. Then they are required to stay 14 days at a location designated by the quarantine station chief (own residence etc.) and to refrain from using public transportation."

https://www.mofa.go.jp/ca/fna/page4e_001053.html

This means that we can't take a connecting flight, or a bus, or even a taxi. The only means I'm aware of for getting back to Kumamoto once we have landed in Japan are 1) having a family member come to pick us up or 2) arranging to rent a car. If there's another method I'm forgetting or unaware of, please let me know.

I'm not sure if they can respond in English but you can call the following number to get confirmation from the Ministry of Health, Labour and Welfare (Kouseishou) as to what you need to do:

0120-565653

Also, you can get support and read about the experiences of other people here:

https://www.facebook.com/groups/returntojapan/

My flight arrived in Narita. I looked for flights into Kansai and Fukuoka but couldn't find anything. Since I was pretty sure that I would get out of customs after the rental agency closed, I planned to stay in the capsule hotel in Narita Airport (9 Hours). When I tried to check in, however, I was told that they don't accept travelers returning from (or coming from) abroad and that something about that was on the Booking.com website. I said that it may have been there but it was not prominent and that there was not any interface that made me confirm that I was not traveling from abroad. The man at the hotel was nice and acknowledged that the interface needs to be improved and said he would refund my money. Fortunately, I was able to get another hotel near the airport. That hotel would not pick me up because I had come in from abroad (government rules -- no "public transportation") but it was close enough to walk to (in the rain 😞 ).

The next day I walked to the Budget Rental office. It was not an easy walk and I could have gotten a ride in the shuttle if I had returned to the airport but I wanted to be there at 9 AM sharp (opening time) to get an early start. Also, even though they said they would come and pick me up it seemed kind of odd to me that a shuttle to the car rental would be OK but a shuttle to a hotel would not.

At the car rental agency I asked why it was so damn expensive (close to 100,000 for the basic fee to Kumamoto, not including tolls and gas). I was told that someone would actually drive the car back to Narita!! Well, that explains the expense.

During the drive back, I became a bit irritated by the "MySOS" app I was compelled to use. My irritation stems from the failure of the people who built it to recognize that it would take me two days to drive back to Kumamoto. This plan was submitted to and approved by the officials at the airport but, apparently, the MySOS app didn't get the memo. The attached image of my possible violation came up on the morning of the 3rd. I was scheduled to arrive in Kumamoto that evening but, according to plan, was still traveling. The app was saying "You should be in Kumamoto today. What the hell are you doing?" My only choice was to tap on OK and continue my trip home. In my view, it shouldn't be rocket science to program travel plans (not just a daily location) into the app.

Another source of irritation was the daily calls I received while driving. In Japan, it's ILLEGAL to talk on the phone while driving. Yet, on both the 2nd and the 3rd I was driving all most all day so, naturally, when they called I was driving. Since the plan was to be driving during those two days, they could have had the app call me a night. Or, they could have figured out a system that would allow me to report in from rest areas when I wasn't driving. But no, they called me on the 2nd and 3rd as though I was sitting at home with nothing to do, waiting for a call.

The phone call only records me looking at the camera. I guess someone could hear me saying "hey, I'm driving" but the "call" was not a conversation. In that sense, it's more like a robocall, but the robot doesn't say anything; it just records your image and (I assume) any sounds you make.

I might have declined to answer the call because I was driving. The problem is, though, that I'm not allowed to call them when it's convenient for me; I can only respond when they call me. That put me in a bit of a bind; do I answer while driving (possibly an illegal act) or risk violating my quarantine (another illegal act that, I was informed, might cause me to get kicked out of Japan completely)?

One more thought: "MySOS" is not an appropriate name for this app. "SOS" is a signal that I would send when I'm in trouble. But, as I wrote, the app doesn't let me contact the authorities that be. I think a better name would be "MyLeash." And, to summarize, it's a leash made by people in Tokyo who obviously didn't take into account the circumstances of people who live far away from Narita.

End of rant. Thanks for reading. :)