After doing some more research about the use and derivation of azana, I've discovered several earlier errors in my translation. In order to clarify things a bit, let's start with the following terms:

字　[あざな]　azana, an informal nickname adopted as a child (小字), or a formal nickname given by one's parents.

氏　[うじ]　uji, the sobriquet you choose for yourself upon reaching your majority; this is a substitute surname, and the name by which you will be commonly addressed as an adult.

本姓　[ほんせい]　honsei, lit. "original name," your surname as originally recorded (registered) upon the census at birth.

姓名　[せいめい]　seimei, or "full name," or honsei + given first name; this is your complete, official name and never changes (sort of like a Social Security number). Traditionally, it was never used publicly, but some, like Rangyoku, use their given name instead of an azana.

Also critical to the discussion is the treatment of your given name in traditional Chinese culture:

According to the Book of Rites, after a man becomes an adult, it is disrespectful for others of the same generation to address him by his given name. Therefore, the given name is reserved for oneself and one's elders, while 字 [zi or ji in Chinese, azana in Japanese] would be used by adults of the same generation to refer to one another in formal occasions or writings; hence the term "courtesy name".

Note the following correction in chapter 2: "His [Chuutatsu's] registered family name was Son (孫) and his original uji, the surname he had chosen at adulthood, was Ken (健)."

This clarifies the following correction in chapter 21, the Royal Kyou addressing Shoukei: "And I take it this is Son (孫) Shou (昭)." Shoukei is enraged by this because the Royal Kyou has condescendingly addressed her by her honsei and without an accompanying honorific. (In Japanese, 昭 would be commonly pronounced "Aki," a girl's first name.)

Shoukei (祥瓊) is in fact her azana, derived from her official given name, Shou (昭). When Youko became empress, she formally adopted the azana, Sekishi (赤子). On the other hand, Keikei is a nickname (小字) or "child's azana" (though there's nothing derogatory about it). His formal name is Rankei (蘭桂).

As David Jordan explains the origins of the 小字 (in this particular context),

Children were sometimes given one or more derogatory nicknames designed to make them seem unattractive so as to avoid their being targets of attack by envious or malicious spirits. These names were, of course, rarely used past childhood, since they were temporary expedients.

Rangyoku is also her formal, given name, not an azana (a mistake I've fixed). As she tells Youko, "Old-timers hate being called by their given first name, but I don't care." Yet even Rangyoku will adopt an uji when she beomes an adult. (Here the etymology seems to part a bit from the Chinese, but the concepts are the same.)

Going back to chapter 2, the Royal Hou Chuutatsu originally took an uji of Ken. The modifier "originally" is necessary because people could take multiple uji throughout their lives. As a minister, his name was Ken Chuutatsu. I am assuming that Chuutatsu (like Sekishi and Shoukei) would have been his azana.

One note about Youko and her alias, Youshi. In Japanese, the trick is easy to pull off because the kanji (陽子) are the same. To avoid confusion, though, I've avoided using Youshi unless the author explicitly indicates that pronunciation, or if a person who only knows her by her alias actually addresses her by name.

UPDATE: It's been pointed out that while Youko's name never comes up in the dialogue in the latter two-thirds of chapter 24, it is written from Rangyoku's POV. I find this a compelling argument, so I'll try substituting in "Youshi" for "Youko" when the narrative meets that criterion.

Labels: 12 kingdoms, honorifics, japanese, language