They have tremendous social solidarity and a sense of responsibility for their fellows - even without a pandemic people with 'the sniffles' will wear a mask outdoors or on the subway for the protection of others.
Well, I have been involved with Japan 50 years, I have not seen much evidence for "a sense of responsibility." Group solidarity kinda died out in 1945. Actually, Americans tend to have more community spirit and more institutions such as clubs, scouting, churches, food banks, people cleaning up local rivers and parks and so on. The Japanese welfare system is miserly, and single mothers in particular are in bad shape these days. However, they do have national healthcare, and the overall quality of it is superb.
The mask on the subway is mainly for the protection of the wearer. It is mainly a muffler to ward off the cold air. In cold weather, when you leave someone's house, they often say, "would you like a mask?" There is a box of them in the foyer. It is true that sick people use them. They are embarrassed to sneeze in public, and they don't want people to their red noses. That's what they tell me, anyway. Not quite the same as responsible, but functionally equivalent.
The Japanese were often impressed by the U.S. cooperative community spirit during the occupation. Example: A man was pushing a cart filled with fruit, which overturned in front of a streetcar. There were several U.S. GI passengers in the streetcar. They jumped out, helped the man to his feet, helped to pick up the fruit, and pushed the cart off to the side. The Japanese passengers would never have thought to do that. They were astounded that any soldiers would. They were deeply impressed.