I'm not agree with number 2 and 3.
Today Japan suffers from economy stagnation, and the future is bleak. I just read a news that written about 2000 Japanese companies go bankrupt recently. So, they have a very difficult problem right now. And that problem is because they can't compete against China. As long as there is the giant China, Japan won't be able to come back from their problem. So Japan must do something.
And remember, Japan has a nostalgia. Where they gloriously beaten Manchu Qing Dynasty. From the 8 alliance, to 1st Sino Japanese War, that end to World War 2. So why not try recreate the past glory and form a new alliance that called "Quad"?
Remember, before world war 2 (actually included world war 1), Japan was the ally of United States.