Thousands of Japanese people marry foreigners every year. Many are happy - but if the marriage breaks down the foreign spouse may end up cut out of the children's lives.
Alex Kahney, who works for a medical publisher, still lives in what was once the family home, now nearly bare of furniture but full of memories.
There are photographs of his daughters on the walls of the small four-storey town house in one of the nicer Tokyo neighbourhoods.
Their favourite stuffed toys, a dog and a mouse, are on the back of the sofa - reminders of the little girls, aged nine and seven, who he has not seen for months.
His Japanese wife took them with her, along with much of the contents of the house, when their marriage broke down, and is refusing to let him see them.
Mr Kahney first tried the police.
But when he told them that his wife had abducted their children, they laughed at him.
What makes it more painful is that their new home is just down the road.
Pressure for change
"They're on a second-floor apartment," he says. "I can hear them talking inside. I go and stand underneath the balcony listening to them. It's tough.
"For the first few months I cried, I howled. For half an hour sometimes. I hardly sleep. I'm usually awake most of the night. And I have dreams, I dream about my children every night."
In Japan, the courts normally give custody to one parent after a marriage breakdown and it is up to that parent if they let the other parent have any access.
Many separating couples come to amicable agreements, but it is not unusual for one parent to be cut out of their children's lives forever.
When the former Prime Minister Junichiro Koizumi divorced, he got custody of his two eldest sons, who have not seen their mother since.
She was six months pregnant at the time, and Mr Koizumi has never met his youngest son.
But now there is pressure for a change in the law.
Every few weeks Alex Kahney joins a demonstration organised by a group called Left-Behind Parents, Japan.
They have lobbied members of the Diet, and on a recent Sunday they marched, more than 100 strong, through the centre of Tokyo.
Among the demonstrators were many Japanese parents.
There are a quarter of a million divorces in Japan every year, which is relatively low by international standards, but a dramatic increase from earlier generations.
It is the cases involving foreigners, though, that are drawing the most attention.
Japan's customs around divorce have become a diplomatic issue because the country has yet to sign up to the 1980 Hague Convention on child abduction. As a result, Japanese parents who bring their children home after a divorce abroad can defy joint custody orders made by foreign courts.
The British embassy is dealing with 38 cases involving children, other embassies many more.
"There are 12 embassies involved in this," says David Warren, the British ambassador in Tokyo.
"We have been making frequent representations to the Japanese government. We've been saying to them that Japan cannot any longer go on without becoming part of the international legal framework for resolving these cases."
Japan is considering ratifying the Hague Convention.
A newspaper report earlier this month said an announcement could come as soon as the spring.
But implementation is likely to be a long process.
It would mean a change from the expectation that families should largely work things out for themselves, to the state enforcing agreements on access and child-support payments.
Some people are also worried that the convention could hinder Japanese trying to flee abusive relationships abroad.
Akiko Oshima is a marriage counsellor who has worked as a mediator in the family court.
"These women who come back, do not do it because they want to," she says.
"They feel this is the only way out. They want their child to be brought up in Japan, and not in the host country where the father is abusive and she has no control over her children's education, and so forth. Not even, say, getting a job to support herself. This is the problem."
Alex Kahney spends a lot of time visiting places he went with his children, like the playground near his home.
He says he was a good parent and his daughters were daddy's girls.
If he is to see them again he must only hope their mother takes pity on him.
- The number of Japanese men marrying foreign women is higher than the number of Japanese women marrying foreign men. It is rare for a Japanese man to marry a Western woman, but Japanese women frequently marry Western men.
- A Japanese man marrying a foreigner is most likely to marry a woman from China, the Philippines or Korea, in that order. A Japanese woman marrying a foreigner is most likely to marry a man from Korea, the US or China.