Japan is not known for specialized medicine and healthcare for the terminally ill, but it does have a very good basic healthcare system that ensures all citizens and non-citizens residing in Japan get their basic health looked after.
Healthcare in Japan is mandatory, but it is also incredibly cheap. You can generally get a very reasonable amount of coverage for a very reasonable price. It costs around 1000 yen per month as a student and not much more as an adult. General check ups, eye exams, and dental health are all covered. You can get blood tests and x-rays for a fraction of what it would cost in America. For example, an x-ray in America would cost around $100-$400 USD average, depending on where you are, and it can climb much higher than that. In Japan, you will rarely pay more than $20 for the same x-ray.
Specialized medicine is a little worse, and rarer genetic conditions are very rarely diagnosed here. I have a friend who has a rare auto-immune disorder, and it went undiagnosed for years while she lived in Japan despite countless doctor visits and exams here. She also reported that as a woman and foreigner, she was not always taken seriously by the doctors, and had to bring her Japanese husband with her as a fortification for her claims.
That being said, the doctor’s words are like God over here. Any back-talking or disagreement with the doctors will get you scolded, and will make the doctor angry with you. But if you can get past a visit without questioning your physician, you can always go to another doctor to get a second opinion. There are no family doctors like in America, and you can move around freely without financial consequence.