Japanese College is a Joke
It's a widely held misconception in the West that Japanese pupils are treated inhumanely. Although school is a slog, it produces a lot of really intelligent and well-educated individuals who are prepared to take on the world. It's also true that kids in Japan have pretty demanding school schedules. They are held to a high standard, and the road to college is not for the timid. But there is a very obvious change once you enter college.
In Japan, college is viewed somewhat humorously by everyone, not just students. It is acknowledged that there is not much to do after graduating from college. The idea that you would procrastinate and barely study is ubiquitous, even in four-year colleges. The goal was college; once you get there, nothing needs to be done. In fact, once you've been accepted, it seems very tough to truly screw up and fail in college. In many regions, the experience is referred to as a vacation.
Employers in Japan frequently solely consider a student's school, not their academic performance. How you did doesn't really matter to them. Additionally, you won't have to write many papers or take many examinations in most universities, so often the hardest part of a course is simply turning up.