Never underestimate the ability of a large corp, with tons of HR staff and lawyer, to skirt and bypass a law like this. The only thing they would do is not come right out and say it that directly. They'd just dress it up as some sort conflict of interest type thing and not be honest about it.
Remember, you as the victim would have get your claim investigated and tried and the deck is painfully stacked against you.
Except this story is about a couple working in a successful startup and not a large corp that has existed for so long that it could have implemented ways of moving around around the law.
This is a quite-misunderstood concept of corporations because all you ever hear about is the big old one in the news so it's natural that you would think that what's happening in the big old ones could happen in any other newer ones.
I could explain quite a lot about how corporation/business works and how it's basically a stupid move on every point to implement an
anti-couple rule, if based in Japan. To your point about lawyers, in Japan, there wouldn't be any lawyer firm that is worth it salt that would accept to work for a business that implement an
anti-couple rule because that's just like shooting yourself in the foot on so many level. It's like if a lawyer firm would accept to work with a business that, in its rule book, allows its upper management to punch their employee in the face whenever they wish for it. Sure, there might be a lot of money to be made out of such a crazy case, but it's counter balanced with how the lawyer firm would simply be unable to protect its client's assets.
And, another point you might not know about: You don't need to put a claim and be tried when it comes to that kind of investigation. While you do have to put in a claim, it's not a claim against the business per say. If you go to a marriage legislation building (the place where you register your marriage), they should have receive some kind of way of communicating about your claim with their upper management who then can request an investment. It's not a case of
victims vs their employer, but
government vs the employer. If the claim is found to be fake, the government has your information through your marriage registration and can fine anyone who exploit the system for no good reason. If the case is found to be valid, then the business is fined for violation and then measures are taken to ensure the rules are changed.
Some big old companies could fight it out in court for years, but that's not the case of any startup as even if they makes a lot of money, they shouldn't be stupid enough to enforce a sooner-then-expected market's curve by wasting funds on corporate rule enforcement instead of expending their market even more. (Especially if it's to enforce staff-detriment rules that could negatively affect the staff well-being.)
I forgot to mention it previously, but there's a legal bypass that exists in Japan.
A foreign entity who launch a local branch of their business (which cost a fortune by the way) in Japan could implement a rule that disallow relationship IF their company in foreign ground has the same rule by extending the corporate rule which, basically, makes Japan recognize the building of the business as a rented space for a foreign entity.
While it's not about the same kind of rules, a good example of the application of this exception is with the US military bases in Japan who have their own rules and laws that are quite different from the ones surrounding the base. That's because the bases are considered rented space for a foreign entity (the US government).
So, an example of how the author could have put a real "anti-couple" rule would have been if, for example, the couple would have been working for a foreign company renting a site in Japan instead of a startup. Not only that would give the company some heavy weight on the financial/power balance, but it would also explain why the rules aren't following the local laws. It could have been a multi-national megacorp from China who rent a space in Japan to hire local engineer in R&D researches toward the mainland's technological advancement would have been believable as, in China, there aren't anti-couple laws for businesses (at least, from what I checked, but I might be wrong). One of the strange part of this kind of exception is the fact that it also give the space immunity against media retaliation.