Romantic as that may be, that’s also ultra super taboo in ancient China. Even the characters of an emperor’s name (and all emperors before him of the same dynasty) is banned from use upon coronation (this was so much of a hassle that some princes changed the spelling of their names just in case if their name contained common characters). Yakwoo, being a eunuch, would have been thoroughly indoctrinated since youth to call the emperor nothing but your majesty
at least a cute pet name... i think the emperor ould like that at least. also isn't this korean? like yes some things are similar in ancient times but maybe not all?
influence of sinosphere.
wait! we never got to see yakwoo call the emperor by name