It means “Your majesty”. Pretty straightforward translation, but still fanfic writer usually use “pyeha” in English language fics, and I prefer it that way. I don’t know why, really. It’s just sounds nice, I guess, and I love the way my favorite character keep saying that word in the drama. 😊

Yes! I love hearing the echo of the characters saying the term. I think that's why I like Hei Lao-ge, now that you mention it: when I see it written, I hear it, just like when I read Shen Wei saying, "Zhao Yunlan," I know exactly what that sounds like. :-)

(I'm pretty sure I kept the transliterated terms in my historical Kdrama fics, for much that reason. :-)