Japan is actually a fairly likely candidate. They were the second nation to close their borders, and they have some crazy healthcare.
Having just suffered through an experience with Japan's healthcare system (still suffering two weeks after the experience, actually), I don't believe that any of Japan's "crazy healthcare" advances have been made available to the public in any significant way. Also, after 90 years of medical research, not a single country in the Known World has found a cure or vaccine for the Rash, and my impression of Nordic healthcare is just as high as some people's impressions of Japanese healthcare, not to mention the many other countries with good healthcare that have become part of the Silent World, so having good healthcare may not be a good indicator for survival.
They're also extremely far from Spain, where the first victims of the illness were, making the chance of infection much lower.
The first publicized cases were of refugees in Spain. We have no way of knowing where it really started. However, it is unlikely that refugees to Spain would come from a place that could also send refugees to Japan. *nods*
They can survive easily on fish and rice.
Fish and rice is not a nutritionally balanced diet, and nowadays Japan imports a lot of rice. Japanese food is supplemented by a variety of foods, many of which are imported. I think if the current generation had to suddenly survive without imports, there would be a lot of hunger and starvation very quickly.
Their biggest problem is the fact that right now they aren't having enough babies, so as old people die, the population will swiftly decrease for the next decade or so. However, in a country where the population density is already extremely high, that could be a benefit.
Yes, the population decline would become an advantage.
Another problem is that the population density would make any possible tourists spread the disease extremely fast. Rural villages and other islands would be almost completely safe, though.
Japan has a
lot of tourists, especially from Europe. The chance of infection from tourists is very high.
Nowadays, rural villages aren't so rural, and are probably not self-sufficient to any significant degree.
There also is Japan's enormous coastline to consider. There are five major countries close enough to Japan for refugees to try to get to Japan, and Japan's military is not big enough to patrol the entire coastline without conscription and taking over fishing boats (neither of which are likely to happen, given Japan's current political and social climate).
Even if Japan miraculously avoided getting the Rash from tourists and refugees, the islands would likely be cut off from one another... I can't imagine anyone in Hokkaido, for instance, being able to trust that a boat arriving from Okinawa is safe. I don't think Japan would be able to stay as one country even if it survived the Rash and the initial starvation period.
Although it would be interesting to see the kind of magic that would be created with Shinto ritualistic practices.