Former senior Japanese diplomat Tanaka Hitoshi, who had known Kissinger for decades, spoke to NHK on Thursday about their relationship. Tanaka is known to have led secret negotiations with North Korea in the early 2000s, which led to a historic bilateral summit and the return of five abducted Japanese nationals.

"He mentioned that he and I had a common interest in preserving secrecy. He knew that I was negotiating with North Korea. And most of them were secret. At one time, he said to me that he had to carry secrets into his own grave and it must be the case with me. I said, yes. My secret may not be as important as his secret, but yet there is a common sort of difficult feeling."

Tanaka also remembers Kissinger as a person who was committed to achieving tangible results when it came to diplomacy.

"He was such a realist. He was a person who was quite successful in producing results in diplomacy. And I used to say, and I'm saying it even today, diplomacy is to do with creating a result. It's not a talk shop. It just needs to create a result. That's what Dr. Kissinger sort of convinced me of. My diplomatic life was very much influenced by him."