"I've accepted that your world is real, so why can't you accept that mine is too?"

This is sort of a depiction of Alfons meeting a younger Ed, one who was still living in Amestris, hence the series-styled clothing.

I thought that it would seem fitting for Ed to say something like this to Alfons, so that Alfons can understand that he needs to accept Amestris, just as he wants Ed to accept Germany.