Yeah. I thought maybe they are considering stopping the underwater human way of life. The society seems to be deteriorating anyway, with lack of children, lack of marriage partners, lack of work... Maybe they are waiting for the appropriate moment to end it all and migrate all the sea people to the dry land. After all, once the (working age) population has dropped below a certain point, they can't anymore maintain a decent quality of life. They would get demoralised well before that, as well.

But since tensions are still high, the time is not yet at hand.

I hope Manaka will invite Tsumugu for a visit at some point. He could just borrow diving equipment like Akari's man.