In the scene in the Taketori Monogatari where the Dainagon ("Great Councillor," Princess Kaguya's third suitor) is ordering his servants to go and get him the five-hued jewel from the dragon's head, there's an interesting textual problem. One of the servants meekly points out that trying to steal part of a dragon might be dangerous, and the Dainagon says something that is usually translated something like this (this is Dickins' translation, because it's available and free):

If ye call yourselves the servants of your lord, even at the peril of your lives are ye bound to do his bidding.

Most Japanese editions of the text will look something like this (this particular one is from the University of Virginia's Japanese Text Initiative):

君の使といはむものは、命を捨てても、己が君の仰言をば叶へむとこそ思ふべけれ。

Dickins' translation seems fairly reasonable, although the original says that a servant should want want to do his lord's bidding. The interesting bit is the first part, though: kimi no tsukai, "servant of [your] lord." The Iwanami Bunko edition of the TM (1970, ed. Sakakura Atsuyoshi 阪倉篤義) actually has a different version of the text:

てんの使といはんものは、命を捨ゝても、をのが君の仰ごとをば叶へんとこそ思ふべけれ。 (p29)

The key difference there is that the first part is not kimi no tsukai but ten no tsukai ("servant of heaven[?]"). There's an endnote about this:

『竹取物語解』は、「てん」を「君」の字の草体から来た誤写として改めるが、「天」をキミと訓むことは、例えば書紀の古訓などにも見えるから、もと「きみの使」の意味で「天の使」と書いたものかもしれない。 (p63)

[Tanaka Ōhide's commentary] Taketori Monogatari Kai argues that ten てん is a mistranscription caused by misreading the cursive form of kimi 君 and corrects the text accordingly, but the reading kimi can be found assigned to the character 天 [usually ten] in older reading traditions for the Nihon shoki and so on, and so it may be that the text was originally 天の使 with the intended meaning kimi no tsukai. (My translation.)

In other words, it may be that a very early scribe wrote 天の使 and intended it to be pronounced kimi no tsukai (modulo 9th-century phonology), but when the tradition of pronouncing 天 kimi died out, we were left with something that looked like it should be pronounced ten no tsukai, the ten of which then came to be written in kana.

It seems to me that this theory is a bit problematic, though; I don't know exactly what part of the Nihon Shoki is being referred to but I strongly suspect that the 天 (literally "heaven") to be read kimi "lord" refers to an Emperor. I doubt that a mere Grand Councillor would dare use 天 to refer to himself, and so it seems unlikely that someone writing this story would put that character in his mouth, so to speak.