When Japanese couples do divorce, litigated resolutions are rare, in part, because the outcomes are so rule driven - absent an agreement of the parties, custody determinations and post-decree payment obligations are very predictable, and the property division rules are at least as clear as they are in the United States (and are almost irrelevant to working class couples with few assets or liabilities).
But, if achieving those ends meant adopting Japanese style child custody laws, and other differences in the Japanese economic and legal millieu that lead to that result (while there is little sex discrimination against unmarried childless women in the Japanese labor market, societal expectations both at home and at work greatly limit the employment participation of married women with children), I'm not sure that many people would be willing to make that tradeoff.
Child Custody In Japan
[In Japan,] Mothers retain custody of the children after divorce in the vast majority of cases, while the non-custodial parent (usually the man) often has little or no contact with the children after the split as joint custody is generally regarded as undesirable in Japan. (One famous case of recent years was ex-prime minister Koizumi Junichiro, who has three sons. After he split with his wife in 1982, he had custody of the elder two sons, who were raised by his sister and have not since seen their mother. She retained custody of the youngest, who was born after the breakup and has never met his father.)
"It's the Japanese general understanding that if they divorce, the noncustodial parent won't be able to see the kid again," says Tokyo divorce lawyer Hiroshi Shibuya, who handles some of the rare cases that are contested. "It's as if the child loses a parent in an accident, as if that parent just dies."
Child support is not normally provided to the ex-wife, meaning she must take on the expense of raising the children herself. This lack of financial support, coupled with little job experience, forces many divorced mothers to move back in with their parents. The result has been an increasing number of divorced Japanese mothers living in poverty regardless of their ex-husband’s financial status.
From here, hat tip to the Red String Comic by Gina Biggs.
As an aside, this isn't a simple matter of "conservatism" regarding family relationships. As best I can tell from Japanese popular culture and non-fiction accounts of living in Japan, few Japanese are a fervently anti-homosexual as many conservative Americans are, although few are as fully accepting of the same sex relationships that deprive parents of grandchildren as the most liberal Americans are either. The Japanese are probably more accepting of adoption and de facto adoption relationships than the average American. Also, there is probably more of a tendency to treat stepsiblings and stepparents are "real parents" in Japan than there is in the United States.
Child Custody In The United States
The American norm in family law (not always honored) is that co-parents remain co-parents of children until they reach adulthood (and beyond, albeit without the same kind of legal supervision). When parents live in the same area, typically the children shuttle between two households spending a couple of nights a week, at least, with each parent. Typically, the arrangement is either an equal number of overnights, or more overnights with a mother who often has a lower income, and modest monthly child support payments until the youngest child reaches adulthood in addition to significant alimony payments in the case of formerly married parents for a year to a few years after a divorce. Often, joint decision making regarding major decisions in children's lives is required.
When never married or no longer married parents live far apart from each other, typically, a significant part of summer vaction and some other long holidays are spent with one parent (typically the father), and the school year is spent with the other (typically the mother), and the child support payment is typically a bit larger.
There are also residual vestiges, in fact, of a now de jure abandoned custody determination consideration called "the tender years doctrine" that preferred the mother of primary custodian of younger children and the father as primary custodian of older children, typically with a divide at about twelve years old. A similar consideration that is sometimes invoked today in American custody cases is the "primary caretaker presumption" that calls for the post-divorce parenting arrangements to mirror those prior to the split up of the parents to the extent practicable, without explicitly invoking the gender of the parent.
Japanese style arrangements are typical in the United States only when an unmarried mother specifically chooses not to identify the paternity of the child as part of a strategy of keeping a father that the mother views as useless or a negative influence out of a child's life, when one of the parents has parental rights terminated for abuse or neglect, or when there is a divorce arising from one spouse abandoning the other, often with whereabouts unknown. More often, it is the dad who is absent, but sometimes, often in cases where the mother has a substance abuse problem, or severe mental health issues, or is in prison, or simply disappears, the mother will be the absent party.
Even in more lopsided cases, typically for good cause described in a contested custody hearing, where one parent has sole decision making authority with respect to the children and the predominant share of parenting time, the other parent is typically granted at least a few days a year of parenting time, perhaps supervised, whether or not that parent wants it. Indeed, absent a termination of parental rights based upon a showing of abuse or neglect by a state attorney in a quasi-criminal proceeding, American judges generally lack the power to entirely deprive a parent of parenting time.
Thus, while it isn't unheard of in the United States for children to lose all contact with one parent, it is almost unheard of for that to happen following a more than momentary marriage of two middle class, respectable people. Likewise, while siblings fairly frequently lose contact with each other if they are left orphans because both of their parents have had their parental rights terminated and they are turned over to the foster care system, it is almost unheard of for siblings to lose contact with each other during childhood in a middle class divorce.
The only kinds of siblings who may infrequently but not too rarely end up without regular contact with their siblings are those where on of the siblings is in juvenile detention, is much older, grown and gone, the siblings are stepsiblings whose parents split up, or the siblings are half-siblings who have never shared a household together.
Now, the American way of handling child custody absolutely has downsides to it. A very large share of joint custody arrangements decreed by U.S. courts result in some additional litigation before the children become adults and this system involves a large share of all minors in the United States at some point in their lives. There are few high school classrooms anywhere in the United States that don't include someone, probably several someones, whose parents haven't been engaged in post-decree litigation at some point. Parental incomes (relevant to child support payment amounts) change, and the fact that kids grow up and need different parenting time arrangements as a result is a near certainty.
A surprisingly large share of unmarried co-parents manage to do a better job of being co-parents than they did as spouses or long term lovers (from experience I'd peg the figure at about two-thirds of separated couples with children), and often (perhaps not quite half the time) have better relationships even with each other with more clearly defined and less personal stakes than they had when they were themselves in a relationship. But, this certainly isn't universal. It is hardly surprising that many divorce or never married couples "don't play well" with each other. A minority of truly high conflict couples fighting over their children perrenially can be a judicial management disaster that is extremely expensive and unpleasant for all involved.
It is also well established that the litigation process itself, and the mere fact of the divorce even when the litigation process isn't that traumatic, is harmful to the children involved outside the very worst, high conflict, domestic violence or criminality tinged marriages.
The parental rights and responsibilties decisions are generally made by a single judge with very limited statutory or case law guidance (the "best interests of the child" standard, interpreted in a fact intense manner on a case by case basis, trumps everything else in the ordinary case), whose has absolute judicial immunity in making that decision. which is not mediated by a jury, judicial panel, or meaningful appellate review. Removing a judge from office is often nearly impossible, even if the judge makes many questionable but not reversable decisions in child custody cases. Even getting a judge off the family court docket is often hard, because there are few volunteers for the post within the judiciary.
This process elicits widespread ire directed towards the system in general and the particular judge involved in making the decision, by a large share of all of the parties who feel dissatisfied with the decision that was made and a significant minority of the parties who are satisfied with the decision that was made by the judge. In that context, any disappointing outcome looks like judicial favoritism and bias.
Most Americans would prefer a regime with more predictability and less judicial discretion than the existing regime. But, not at the expensive of determinations that were as lopsided as those in Japan.
While full marriages end easily in the United States, co-parent relationships are very hard to end. We don't call it that, but the American serial monogamy system verges on an almost polygamy system when ex-spouses have shared children. All second spouses of both parties end of having some sort of relationship with the first spouses of both parents at the very practical level of being de facto co-parents of the same children. Children of unmarried and separated parents inevitably have de jure or de facto stepsiblings with whom they must develop relationships of some kind. All the parents and stepparents involved are one complicated extended family.
But, generally, we see the problems of managing these complicated separated and blended family arrangements as an inevitable consequence of the fact that parents can't always manage to keep their relationships together. Americans may argue for measures to discourage divorce in couples with children, or to reduce harm in the family law litigation process, but nobody is arguing that depriving children completely of contact with one of their two parents or their siblings, without a very good, fault based reason is conscionable.
Indeed, increasingly, we are a nation having doubts about even the concept of a closed adoption, where adopted children have no contact with their birth parents. In Britain, controversy is raging over the practical problem of avoiding incest when many children have genetic fathers who are the same undisclosed sperm donor. The modern trend is to see genetic relationships, while not controlling of what the relationship should be, as an undeniable basis of some relationship that gives rise to mutual obligations between all parents and all children.
After decades of frequent divorce (although it is less common now for middle class families than it used to be), there is still not a consensus on what kind of relationships the people involved should have with each other, how parenting should be arranged with similarily situated families, how inheritances should be handled when people consciously choose to write wills and trusts to distribute their wealthy in blended family situations, or an any other particular substantive or procedural reform of the system.
A minority want to return to the fault based regime that we once had for almost a century between the no divorce era and the divorce on demand era of "no fault", but where "covenant marriages" that include that option are available, they are rarely chosen.
The fact that the status quo is problematic is widespread, but there is little criticism of it that isn't so deeply embroiled in personal negative experiences that one can have much hope that it could be widely applied.
Also, while the Japanese extreme seems harsh and unconscionable even, it is hard to tell if it is really worse. In a society where divorce is so rare, the situation of divorced children in Japan may not be an apples to apples comparison with divorced children in the United States. There is no real consensus means of determining what psychological impact a divorce has on children and no obvious way to compare existing outcomes with counterfactual alternatives.