In 2050, polygamy became legal in Japan. A man could have up to four wives, and wives were obliged to devote themselves to their husbands. The reason why husbands can break up with their wives who disobeyed them even a little is because of polygamy. That's why wives desperately support their husbands, wanting to have children as soon as possible and snuggling up to their husbands. It's a harem for men.
