One thing, that does not get discussed here is the stigma in Japan in the community if anyone has been found to be infected with some serious disease. E.g. if one of your neighbors gets infected with A, then their family would be forever associated with that disease. So, many people would just avoid visiting a doctor at any cost for fear of being just known as the Covid-19 patients. There was the story on Japanese news about someone who was on Diamond Princess and tested negative but still being harassed by his neighbors.
Second thing, that has not been discussed is that in Japan generally people try to not stand out by being ill or missing out on work, which is often mistaken for being considerate of others. If anyone has seen the full parks in recent weeks and full trains, then one could be convinced that Japanese are largely egoistic.
Third thing, is that Japan has a test rate lower than countries of world economic stature such as Moldova, Nepal and Cuba. Even though that the prime minister Abe promised that they would increase tests performed to 20,000 a day, in the last week, in Japan there have been 25,000 PCR test performed. Less you test, fewer people you would find even though we see many people are asymptomatic and infecting vulnerable people.
Forth thing, according to some article in Nature, Japan does not perform post mortem autopsies. Only 1.6% have undergone such procedure in mid 2010s. So, even if you die from an accompanying disease such as pneumonia, it is hard to find if the Covid-19 really triggered it if no one is testing. So, now the cases which are announced as deaths from coronavirus have to do only with people who tested positive before their passing. I read also that Japan reports pneumonia deaths every three year, conveniently next report is due in 2 years.
Fifth thing, as @Pandaazuma correctly points out, but since has disappeared, that in 2011 there was fingerprinting at Japan and worries that Japan was trying to cover up the real tragedy at Fukushima. He, unfortunately, does not recall that only when a field team from IAAE was about to visit the plant site, the Japanese government changed the story - from just steam to meltdown at two reactors. Almost everyone I knew left the country or Tokyo area at that time. Sumo-related, I know for a fact that Naruto-oyakata, a proud Japanese now, fled Tokyo then (my source is someone who hosted him). I am sure at that time many other masculine rikishis had fled Tokyo as well.
Sixth thing, Japan's constitution does not allow for US or EU styled lockdowns. So, there are just recommendations and urges by the government and they rely on the local, prefectural, governments to take on the initiative. But unfortunately Koike in Tokyo is as indecisive as the prime minister. At first no worries and messages such as "cherry viewing is to Japanese what hugging is to Italians", and no hanami bans in the first weeks to worried looks and message just right after Olympics were postponed. By the way, no bans on travelers from China and Wuhan were imposed even though the virus was known to be circulating there etc because Japanese wanted to cash in on the Chinese travellers during the Lunar New Year travels.............Government and so on could be accused of derelict of duty.
Seven thing, the last time any embassy recommended leaving the country immediately was in 2011. One of the European embassies in their newsletter accused Japan of providing false information in March (I do not have the link anymore), which was last observed in 2011.
Eight things, despite the Japanese pride in their healthcare system, it seems it is rather unprepared to tackles a crisis such as pandemic. Not enough ICU beds, not enough ventillators. So what do you then? Many hospitals turn away patients for fear of being seen as a hospital with a Covid 19 patient or not being prepared to treat one. 4 months have passed and instead of taking lessons from S. Korea, Taiwan, who had endured SARS pandemics, Japan just wasted tame on identifying clusters and trying to keep on hosting the Olympics in July. Tokyo is at 271% occupation rate for ICU beds at the beginning of the second week of the emergency proclamation.
And many others but this is sumo forum, so:
I read most posts on Twitter related to the infected rikishi - most people miraculously tend to agree that the silence from NSK on the matter - who the rikishi is and which the beya - is astounding and resembles the silence during the yaocho scandal. In my mind and my experience with Japan, it has to do with "who is going to pay for it?" question and NSK does not want to lose any income from NHK so I believe they would push for Natsu basho at any cost. (Why it matters - NSK is a public interest incorporated organization/foundation - so if they hide the information, the public interest might be their profit only!)
Anyhow, I just read this story from Yahoo JP that during the Taiwan (under Japanese occupation at that time) jungyo in April 1918, three rikishis got infected with Spanish flu and passed away. More than 20 rikishes fell ill from the disease, which was known for some time as sumo flu.