When Japanese children grow up, they're under tremendous pressure to succeed. Companies usually hire new employees from one or two specific universities, maybe 200-500 new hires at a time. Therefore, if you want to get into a specific company you need to know what university they hire from. Then, the universities usually only accept applicants from specific high schools. So, you're now looking for the pre-school that's most likely to get you into the high school you want. You want to talk about stress - Japanese kids can have their entire future planned out by age 6, and they're going to be working hard all along the way to compete against everyone else also trying to get into those schools and companies, and not everyone is going to make the cut.
For this reason, Japanese adults are very lenient towards young children. "Let the kids play now, while they have the chance". They're unlikely to rein their kids in if they get too loud or boisterous. But, there's a one more exception to the rules of proper behavior. And that's when you get into college. If you make it into a university, you're pretty much guaranteed to get hired when you graduate, plus the company is going to put you into a multi-year training program to indoctrinate you into its ranks, so there's little real reason to study at this point. College becomes a 4-year vacation, and college students usually use this time to lose themselves in their hobbies, like making model figures of anime characters or pop idols, to form dancing groups that perform in Yoyogi park, or to form a band.
This means that the most eccentric people you're going to meet in Japan are college students, because the rest of society knows that this is the only time those kids are going to have to "be themselves". The day of reckoning will come once they enter the role of "corporate drone" when their college freedoms will get yanked away from them. In the meantime, no one will berate a college male for reading "Nakayoshi" magazine on the train.