"Justiciar" is good, I like that. I'll have to look up how close etymologically it is to "dispenser of justice," which does not seem to be the Regent's strong point...

angsty post-canon fic where Chu Shuzhi is promoted to the position of Dixing Ambassador and has to decide how he wants to be addressed and how to present himself
ooh, interesting, I would definitely read that. One reason I like "Envoy" in English is because it can mean "ambassador" but also suggests more possible nuances...