in a nutshell, the empress ranks much higher compared to the queen. we can say that the empress is the legal wife or consort whilst the queen is the second wife.
Empress has a higher standing usually first wife
Queen has a lower standing, second wife
Kings marry multiple people for more political power, alliances with other countries and stuff like that
The queen and empress thing is in reference to this comic specifically.
Ah, so judging by the appearance of the empress and Queen, the emperor is a really old man who married a young queen?
maybe. but he's the emperor anyways, he's free to marry any unmarried woman (as long as they already had their debut in high society)
I'm a bit confused, what's the difference between empress and Queen, and are they married to the same person? I think I'm missing some parts.