The Kami plane works in an intriguing fashion. It can wipe out memories of
mortals who found their way to it, but it cannot remove the PHYSICAL
evidence of their existence. This means every photo and every public record
of them still exist. All this is something Ranma can use to show the
existence of Akane, right?
Then there is the matter of the time synchronization of the kami plane and
the mortal plane, you're leading up to something with that aren't you?