Basically, people are not desperate about socializing. If you want to make friends, do it. If not, you don't have to, especially in big cities. How hard depends on - your Japanese language skill - how hard you are trying to assimilate - your attitude - if you belong to local communities and so on. Those who are overly self-conscious people tent to be laughed at.
Since there are some differences between Japan and other countries, it might be a bit difficult for people from other countries to make friends. I was born and raised in Japan, and of course, I can speak Japanese fluently. Even for me, it is not easy to make friends when moving to a different place. Now I live in a foreign country. My feeling is that making friends here is far easier than doing it in Japan despite that my English is not so good. Being humble is important in Japan, but when you are very humble you can't socialise so much. This is like a conundrum.