There was an American who had dived together in Yonaguni, who was likely a CIA officer, but not for sure. He at least introduced himself as a US military contractor, who spent a day off in that island.
There are several bases in Okinawa, hence its explanation was quite reasonable. The only issue was he needed to transit his flight once, traveling to this west end of the Okinawa islands, though not irregular destination for the diving vacation.
I asked him more about what he worked as a consult and realized he was a consultant whose job was dominated by Japanese companies. I thought his identity was fake at the spot.
I had realized the US had tracked me for a long time, as they accessed actually what I wrote from the US military server. I did not check who they were anymore, though I used to be interested in my readers, some of those were from the Japanese central government about tens of percent of total and some others from oversea.
That was why I though he worked for the CIA at the spot as well, but could not confirm as there was enough possibility that he really worked for the US military. In any way, he was related to the US government and I thought he was sent to monitor me. The majority of people on the board assumed I was there to contact him, not for diving, as just two of us spoke in English.
I am not sure what he actually told to do, but it was just a monitor on the boat, as there was a European spy at my hotel. In this way, they could share the monitor, not to be revealed their true purpose. On the other hand, the undercover police officer was eager to know who he was as he could not understand what we talked there.
However, they were ultimately sent by the same group and the same purpose, which they just did not know what they were doing. The intelligence joint operation was conducted in this manner at the ground level.