The neurodegenerative disease, which has no known cure, had progressed to such a degree that Hayashi was effectively unable to move and required 24-hour assistance.

Investigators believe that Okubo first replied to one of Hayashi’s messages about 11 months before her death and offered to help her – and that her reply was that his offer made her “cry from happiness”.

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On the day of her death, Hayashi told her carer that some friends were coming. They left just 10 minutes later and her assistant found that she had lapsed into unconsciousness. She was pronounced dead at a local hospital soon afterwards.

It was later reported that Hayashi had transferred 1 million yen (US$9,500) to an account associated with Okubo a few days before her death.

Neither euthanasia nor “dignified death” – the withholding of treatment that would otherwise prolong a person’s life – are clearly defined under Japanese law and the entire issue is “extremely complicated”, said Yasuyuki Gondo, a psychologist at Osaka University who specialises in elderly patients.

“In Japan, there is a long tradition of caring for people, even when they are bedridden, but there has been some debate on ending the life of a person who is unconscious and only being fed through a tube, for example,” he said. “But there is nothing approaching a consensus on what should be done.”

The question becomes even more complicated when the individual is younger, he said, while Japanese family dynamics also come into play.

“In research that we have carried out, the majority of old people say they are afraid of being a burden on their families or their children and that they would rather not be alive than to feel that they were inconveniencing others,” he said.

“But it is very difficult to confirm that is actually how they feel and that they would prefer to die than be a burden.”

A number of surveys have indicated that between 70 per cent and 80 per cent of the Japanese public are in favour of legislation that would make euthanasia legal, as it is in Switzerland, the Netherlands and a number of other countries, according to the Japanese Society for Dying with Dignity.

The organisation, which is a vocal campaigner for a person’s right to refuse care if they have a terminal medical condition and encourages people to create a “living will” to spell out how they wish to spend their final days, said in a statement that Japan “should not accept euthanasia before a change in awareness and a reform of the rules on living wills”, adding that self-determination on the end of a person’s life is “the pursuit of happiness and therefore guaranteed by the constitution”.

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“We hope that this issue will lift the taboo that surrounds the question of death with dignity and encourage discussion on the right to die,” it said.

Gondo the psychologist, however, said he thinks that a change is unlikely to come any time soon.

“We have had these discussions in the past, when other people have assisted another person’s death, but it is soon forgotten again,” he said. “Also, politics here is still dominated by conservatives and mainstream-thinkers and they are reluctant to even consider this matter – they say that a long life is always a treasure and never a burden.”

Hayashi’s father, Kazuo Hayashi, has condemned the doctor who ended his daughter’s life and said he had no idea that she was so desperate to die.

“I would definitely have stopped her if I had known,” he told the Asahi newspaper. “I don’t think there is a parent anywhere who would give their consent.”

Saying he had “no idea why [the doctors] did what they did”, he described their arrest as “only to be expected”, adding: “how could they take money by taking advantage of the weakness of an individual?”