When a romantic adventure becomes a nightmare ...

Marrying into a culture as foreign as Japan's is about the most reckless emotional adventure one can conceive of, the equivalent of crossing the Pacific in a barrel or attempting to fly without benefit of wings. I know, I did it.

Of course, that's not how it seems to begin with. You and your partner have different looks and different languages, but these are differences that young love bridges readily. Often they give the relationship a special spice. But far more treacherous and difficult to negotiate are the problems that derive from different cultural expectations.

In the West, a marriage is a matter almost exclusively for the couple concerned, providing they are above the age of discretion. In-laws, on the whole, may like their son's/daughter's choice or lump it. Even when lineage matters furiously, as amongst royals and bluebloods, parental opinion holds far less sway than it used to. Marriage in the West, after all, is a liaison of individuals.

By contrast, the foreigner who falls in love and marries a Japanese finds himself with an interesting walk-on role in a rather different sort of drama. Historically, marriage in Japan was the liaison only incidentally of individuals: much more importantly it was about the conjoining of families and the production of heirs. If the Japanese family happen to be particularly modern-minded, or poor, or if there are already two or three boy-children crawling around, a prospective husband may not notice much difference. But if, as in the case of the unfortunate Brian Thomas, these factors do not apply, the diverting cross-cultural experience can rapidly turn into a nightmare of conflicting hopes and expectations.

In the Japanese system, when there is family money, or land, or a business to be passed down, it is enormously important for there to be a boy child to inherit it. Ideally, the line of descent goes from father to son to grandson. But if there is no son, or the son is unproductive, it can go father-daughter-son. In that case, however, the daughter's husband must submit to being adopted into his wife's family, taking his wife's surname, and generally deferring to his wife's family's wishes.

A man adopted like this into his wife's family is known in Japanese as yoshi, and it is a deeply unenviable role: the subservience required is much like that expected of the traditional Japanese wife. One can only speculate as to why Brian Thomas has not been allowed to play such a role, and thus play a part in the rearing of his child. Perhaps the issue was argued back and forth - the question of whether or not he could be relied on to submit to the yoshi's role, with all its inherent humiliations - and the tough conclusion reached that he could not. With the brutal decisiveness which the Japanese can sometimes display in settling emotional questions, he was duly shut out, for ever.

Japanese attitudes towards marrying out have liberalised enormously in the past 30 years. So it was probably not Mr Thomas's Welshness that counted against him, any more than his son's half-Welshness will prevent him inheriting the family fortune. What matters is that the family line is perpetuated - regardless of the emotional costs to those involved.