For your information, Japanese students have access to financial aid in the form of grants or low-interest loans to help cover the costs of university -- my cousins had access to these when they attended university years ago. So it's not as if Japanese students have no hope whatsoever to support themselves if they are a student.
[As an aside, I believe I have this disclosed this already, but I am half-American, half-Japanese, and am a dual Canadian/American citizen.]
Well, I'm Japanese and I know the situation well.
If you are extremely poor, then most of the time, tuition fees are exempted to some degrees, depending on the level of poverty. And yes, Japan also do have low-interest loans. Grants? Not so much. It is usually specialized or has some sort of restriction for applying, or there may be a restriction that applies after you finished getting your degree.
The problem is, all these grants are for people who are in middle class to extreme poverty. It doesn't really matter how smart you are, if you don't meet the criteria, then you can't get them. One of the complicated situation is where your parents, despite being wealthy, won't let you go to college. If you are smart and can get some sort of scholarships, then you don't need your parents to go to college. In Japan, it doesn't work that way. If your parents are rich, and they won't pay, then there's really no other way get enough money to go to college other than working at the same time, or getting a job then go to college.
Loans are actually quite complicated. If you are underaged, you need your parents' consent. If you parents refuse, then you'll have to use the surety company. That comes with more complications. Some loans ask you to be financially independent, which requires some paperwork that includes your parents having to have to do something. If they refuse, then you can't do anything about it.
I've actually lived a year working while going to college to pay full of my fees. Boy, that was tough. My parents and I had some arguments over a lot of things, and they basically disowned me (there is no legal way to disown, so it remains informal). Scholarships and low-interest loan didn't work because I needed information on my parents' income, which my parents refused to give me. My parents were fairly rich too, so I really had no hope of having some sort of exemption or getting scholarships. Eventually, my siblings mediated and now my parents and I are on good terms. They also paid for my master's course (in Japan, Ph.D course and Masters course is separate). But I lived off wasted food of convenience store that I worked in during my undergrad course. I wonder what would've happened if I didn't live in the dorms (much cheaper). I'm in Ph.D course right now and I am one of those few that gets paid by the government, so I don't need to worry about my parents anymore. I did work my ass off to get that, though.
I did tons of research on this. Trust me. It's not as simple as it may seem if you look at the details.