Mr Sakai is not a right-wing militarist who saw the loss of his sword as a symbol of emasculation by the Allies after the war, and has been seething ever since. On the contrary, he has what he refers to as 'socialist tendencies' - he talks about his politics in a hushed voice, as if the 'tendencies' were something more shameful, liable to prosecution even.
And it turns out that he suffered once for his 'tendencies'. In the 1930s, as Japan infused itself with fascism and the dream of conquering East Asia militarily, Mr Sakai, who was a teacher, tried to organise a clandestine teachers' trade union. This was illegal, and he was discovered, arrested and spent 40 days in prison. After his release he was banned from teaching, and he taught himself how to fix and operate radio sets to earn a living. Eventually he got a job as a radio operator on a Japanese cargo ship that plied the Pacific as far as the west coast of the United States.
Then war broke out, and he was drafted: because of his radio and sailing expertise he was sent to Singapore to work as a radio operator on Japanese patrol boats in the Malacca Straits and the Indian Ocean. Before leaving Japan his uncle gave him the sword: one of the finely tempered steel samurai swords with a blade so sharp it will slice paper cleanly in the air. One antique Japanese sword was sold for pounds 250,000 at auction in April.
Mr Sakai was lucky to survive the war. One night his boat was patrolling the Straits between Malaysia and Sumatra when it was hit by a torpedo - he thinks from a US submarine. He spent the night in the sea, some of his fellow crew members were drowned, and the remainder were picked up the next morning by another Japanese ship. Already the signs were bad for Japan's war effort. 'We were foolish, we all believed in the war at the start - even I, a socialist. We thought final victory would be ours. But when the bad news started we reflected deeply.'
The news got worse and worse as the Allies counter-attacked throughout East Asia and the Pacific, and in the middle of 1945 Mr Sakai was taken prisoner, along with thousands of others, in Malaysia. He was held in a rubber plantation outside Kuala Lumpur, in a place that was called, he thinks, Layang Layang. The Englishman who ran the plantation, Mr Pennyfather, had apparently left before the Japanese took Malaysia.
Mr Sakai still had his sword and a pistol, but knew that the Japanese prisoners were to be disarmed at Kuala Lumpur airport.
'I did not want to give up my sword to the soldiers at the airport, where it would be thrown on a heap and probably melted down for scrap metal. It was a work of art. It had a beautiful engraving of a dragon on the blade. It was very beautiful.' As he spoke, Mr Sakai took out a sheet of paper and sketched the sword with reverent, lingering strokes of a pencil.
He gave the sword to the Indian overseer of the plantation, with instructions to give it to Mr Pennyfather when he returned as a gift for the 'hospitality' on his estate. He also got rid of his pistol. 'At that time, I didn't know whether I was to be shot or not. But I did not want it to happen with my own gun.' So he took out the firing pin and threw it in a pond, and buried the rest.
When Mr Sakai arrived in Kuala Lumpur, all he had with him was his watch and lighter. He remembers a Scottish soldier who took his watch: 'I was patriotic. He asked me if the watch kept good time, and I said 'Yes, it is a good quality Japanese watch'. If I had said it was unreliable, he would not have taken it.'
But he bears no resentment against the Allies: based on the way his countrymen had treated their prisoners of war, he had expected to be sent to a labour camp 'in Africa or some other place for the rest of my life. We were delighted that they repatriated us to Japan. They treated us very properly.'
But Mr Sakai has never found out what happened to his sword. He thought at the time that the Indian overseer was trustworthy, but he has since had his doubts whether the sword ever reached Mr Pennyfather. 'Such a beautiful sword,' he repeated, wistfully.