The most likely and obvious foreshadow is that when Kako disappeared without a trace, with no body being even found, she probably went to the future. And now the older Kako is using the same time-travel technology to reminisce or something on the past when Nozomi was younger. (Hence Nozomi being able to recognise future-Kako despite the difference). It was also explained in a
previous chapter that it is illegal to travel to a period where one existed, with the minimum sentence being life imprisonment, which is why future-Kako appeared conveniently after present-Kako left the chapter.
Maybe Kako invented time-travel in her future because there's already an international team investigating artefacts from the future, which includes her mother, and yada-yada, Kako has to invent time-travel by reverse-engineering the future artefacts in the present to get back her family after they get arrested by the time police or something. Or maybe that's too high stakes for a low stakes story.