The High Ki of Twi are the ultimate rulers of their mysterious twinned kingdom.
Like all other inhabitants of Twi, the High Ki consists of a set of twins. They are petite and beautiful young women, with fair skin, blue eyes, and flowing brown hair. They wear delicate crowns of gold filigree, and dress in the royal colors of Twi, yellow trimmed with green. As is normal in Twi, they think and speak and act in unison.
Since the High Ki only rule when their subsidiaries, the Ki of Twi and the Ki-Ki of Twi, cannot agree, there is normally little for the young women to do. During a brief period when Prince Marvel visited their country, the High Ki twins were separated into individual people by fairy magic. (One of the twins proved to be a talented musician, which implies that the other is too.) Their separate state proving unsatisfactory, both twins were glad to be re-united.
After traveling around Yew with Prince Marvel and sharing in his exploits, the High Ki of Twi returned home. The gap in their border hedge was blocked up, and they and their people returned to their prior isolation. (The Enchanted Island of Yew)
Since the land of Twi derives its name from its state of perpetual twilight, it seems clear that the title "High Ki of Twi" is an exercise in assonance and rhyme.