'Our food had run out. By then I weighed less than 30kg and, like the other troops, I was eating the flesh of dead enemy soldiers just to stay alive,' he told The Age newspaper.

'Those who were strong enough were evacuating from the coast, deserting the weak and ordering them to keep the Australians and Americans at bay. So I said to the soldiers left behind, 'No matter what happens, if you die in this land I will come back for you, and I'll return you to Japan to rest with your families. This is my promise to you'.'

It was while walking the Kokoda Track, where the other 55 members of Mr Nishimura's 56-strong platoon were killed, that author Charles Happell first heard the old soldier's extraordinary and largely untold story.

His new book, The Bone Man of Kokoda, offers a new perspective on the legend of a celebrated trail that has become a rite of passage for Australians, and synonymous with their national identity. Bloody fighting along Kokoda marked a turning point in the Pacific war, halting the Imperial Army's relentless push south. Many of the 3,095 Allied troops who perished were given proper burials but the Japanese government, humiliated by defeat, made virtually no effort to recover the remains of its 13,000 victims.

Mr Nishimura, who was wounded three times in the shoulder and survived the later sinking of a boat off Taiwan, always regarded it as his duty to rescue soldiers he said were 'left to rot'.

In post-war Japan, he built up a successful and respected engineering business, developing lightweight steel rods widely used in house construction. He counted Sony founder Akio Morita among his influential friends. But Mr Nishimura remained determined to carry out his promise and in 1979, when he retired aged 60, he told his shocked family he was leaving. His furious wife and two grown-up sons left their house that night, while daughter Sachiko sided with her father.

'His wife said he was crazy and his two sons thought it was too dangerous,' Happell says. 'To this day neither Kokichi nor Sachiko have spoken to the other half of the family. They don't know what they're doing or if they're still alive.'

Mr Nishimura said he didn't give a moment's thought to his estranged loved ones during the 26-year quest.

Armed with just a metal detector, pick and shovel, he arrived in Papua New Guinea and built a two-storey wooden house on a small plot of land. But he was happiest when camping for weeks at a time in areas where bones, dog tags and small metal lunch boxes were plentiful.

'The bodies were rarely buried deeper than a metre,' writes Happell in his book. 'Often, soldiers just dropped where they were shot; occasionally they were spread-eagled on top of each other.'

When he finally made it to Efogi, where most of his platoon comrades were wiped out at the Battle of Brigade Hill, all he found was some charred bones and black soil. To get rid of the unbearable stench, Australian soldiers had burned hundreds of the rotting bodies.

For Mr Nishimura it was a devastating discovery, but he collected some ash which is now housed at a shrine in Japan. 'At least I know my old friends are resting safely back at their home with their families,' he says.

While the old soldier has been able to present grateful families with the remains of their loved ones, he says the Japanese government has been an obstacle. They knew of, but did nothing about, macabre displays of soldiers' skulls and possessions on show for tourists in some parts of Papua New Guinea.

To mark the 50th anniversary of the war's end in 1995, the Japanese ambassador invited him to hand over the bone collection, assuring him identification efforts would be made. Instead, Happell says, DNA tests were never conducted. 'The bones were taken to a cemetery for the unknown war dead.'

In Japan, Mr Nishimura enjoys minor notoriety, being regarded as something of a maverick by those who have heard his story. The Age newspaper paints an affectionate picture of a stubborn and bloody-minded character totally obsessed by his sense of honour, duty and loyalty to those who didn't survive their collective wartime hell.

'You might see it as a big sacrifice to lose your family,' he says. 'But what sort of sacrifice is it against that made by the soldiers who died in New Guinea? Compared to them, I live in heaven. Those soldiers were in hell, and they died in hell. I was one of the very lucky ones ... digging up bones for 26 years was quite a small thing, a small sacrifice. I owed them that at the very least.'

Mr Nishimura was a proud conscript who saw little action in the triumphant weeks following the attack on Pearl Harbour as the 144th regiment swept through the Pacific islands of Guam and New Britain.

But the ill-conceived invasion of New Guinea that followed exposed the naive grenade launcher to the full horror of war.

Soldiers were faced with a torturous 100km trek through humid and malaria-infested jungle before negotiating the mountainous 96km Kokoda Track to Port Moresby.

The heavy fighting against retreating Australian troops took a terrible toll.

During the Battle of Brigade Hill that wiped out most of his platoon, Mr Nishimura was attacked by a young Australian soldier who fired his machine gun at point blank range. Three bullets ricocheted off his helmet and lodged in his shoulder.

Mr Nishimura chased his assailant into the jungle. In the ensuing struggle, he plunged a sword into the Australian's stomach.

'The soldier let out a siren-like wail and that kept Nishimura awake at night for years,' says Happell.

Some Japanese soldiers, including Mr Nishimura, may have made it to within sight of the heavily fortified island capital, but after Allied air attacks decimated supply lines, their commanders ordered a withdrawal.

Within weeks, the retreating and disoriented army was wracked by starvation and deadly diseases like malaria, dengue fever and scrub typhus.

Widespread cannibalism set in. Japanese soldiers referred to the flesh of dead Australian and Americans as 'white pork' while indigenous islanders who had been forced into slavery were called 'black pork'.

'No one who was [there] could have survived that siege without eating human flesh, and that was the truth of it,' Mr Nishimura told the author.

'Nobody wanted to do it, but that was their last resort. It was eat, or die.'

It's not clear exactly how the old soldier, who now lives with his daughter just north of Tokyo, feels about the army he served in and the many war crimes it committed across Asia and the Pacific.

In the book, Happell says, Mr Nishimura was aware of atrocities committed against villagers when he returned to Papua New Guinea. '[He] wanted to show the Papuans that the Japanese were not all pitiless warmongers capable of unspeakable barbarity.'

Mr Nishimura also ponders the futility of war, expressing his emotions after killing the young Australian. 'By the good grace of some divine force, I am here alive and he is there, dead. Where is the good sense in being involved in a war that metes out justice in this totally arbitrary way? Why did I have to kill this young man who has a family just as I have?'

Happell believes Mr Nishimura's deeds are at odds with the army's brutal reputation.

'That was a barbaric army. They had an uncommon bloodlust,' he says. 'But it would be wrong to demonise every soldier, and Nishimura's humanity is proof of that.'