All Japanese and Spanish people I know:

"Can't find/not interested in a partner"

"Can't afford children"

"Haven't got time for children"

"You can always go in-vitro"

In Japan, as in other places like Spain, people have chosen to keep propping up many social and economic institutions that are directly anti-birth and anti-family, for the sake of a given social order. As I said in another note, human societies make the choices, and then nature self-regulates.

Japan's current lifestyle, like Spain's, is a recipe for demographic extinction. There are many reasons why individuals may make a strictly rational personal choice to go along with it, and I don't oppose that.

I'm just saying that at the collective level, societies that choose that path simply go extinct and eventually either disappear completely replaced by others, or reverse course and change their ways.