After all these explanations of the details of Japanese life, I thought it might be worth trying some larger theories for a change.
One thing I find is little written about but explains a lot is trying to avoid awkward conversations with your colleagues, fellow mothers, distant family, etc. If you go on holiday to Guam or Paris, make sure you see all the famous landmarks and take photos in front of them, bring back macadamia nut chocolates, use well-known airlines and other travel companies, study English, do the usual hobbies, etc etc, no explanation will be needed when you mention those things and so you can get back to the comfort of polite chat and meaningless fixed phrases.
Mention that you are studying Swahili, volunteering to help the homeless, taking an interest in religion, etc etc, and you will be asked for detailed reasons why. Not only will that take you off the comfortable limits of polite Japanese conversation, but you will also notice your conversation partner storing every detail of what you say. Why might that be? To tell other people, of course – because gossiping about other people’s peculiarities is another great way of avoiding uncomfortable conversation about yourself.