Here! THAT'S IT! You've come up with the perfect plot for yourself! Think about it, if giantesses can't travel by transport and trade with other continents is impossible, then this is where politics should come in between the world of giantesses and the world where the main character came from. But think for yourself, given the size of the girls, they can easily create ships or planes for ordinary people, and those can establish trade with other giantesses for them or install sinks to teleport giantesses to a new continent. In fact, it will be mutually beneficial for both sides! In fact, girls will be able to start relationships and have children again (well, having sex is more or less normal if our pink-haired inventor can improve the reduction system or at least extend it), trade and communication with other girls will be established, technology can be introduced again, and so on! You have a plot that basically gets into your hands! Patty's teleport is essentially the solution to all the girls' problems (and I'm not just talking about mixing between islands) It will breathe life back into the world of giantesses, and it will be even more fun. Of course, not every guy wants to live among giantesses, but I think there will be enthusiasts and interested parties in this + giantesses' resources and technologies over these 500 years...it seems that you may soon have a good story or even more.