Japanese men are on an anti-marriage and anti-cohabitation strike due to feminism and its usual push for a rising divorce/cohabitation rate. ...much more of a factor than fewer men in the population.
I don't think so. The phenomenon is young Japanese women living with parents, rent free, with good jobs and lots of money to spend on luxury goods.
They see traditional marriage as a trap, where the wife is expected to stay home, take care of the kids, waiting for hubby to return from a night of drinking with fellow office workers.
The husband returns, to issue one word orders to his subservient wife - meshi (food), furo (bath), neru (sleep).
Until Japanese men adopt a more Western attitude toward sharing the family chores, Japan will suffer.