The Japanese terms for nobility that Ono uses are derived from medieval Chinese peerage. However, their English equivalents do have historical precedence. In the early Meiji period, Japanese nobility below that of emperor was officially designated as follows: prince, marquis, count, viscount, and baron. It was also during this time that the design of the revised constitutional system was being drawn heavily from the Prussian model, so the adoption of these European terms is hardly surprising.

王　[おう]　king/emperor/empress
公　[こう]　kou, prince of the realm (the same kou as in Sankou: the minsters of right, left, and privy seal)
侯　[こう]　kou, province lord (marquis)
伯　[はく]　haku, count (same as British earl) or minister
　卿伯　[けいはく]　keihaku, undersecretary or vice minister
卿　[けい]　kei, province minister (viscount)
大夫　[だいぶ]　daibu, baron
　上中下　three subdivisions of baron: upper, middle, lower
士　[し]　knight (samurai) or gentleman
　上中下　three subdivisions of knight: upper, middle, lower

飛仙　[ひせん]　hisen, lit. "flying wizard" or wizard of the air.
地仙　[ちせん]　chisen, lit. "earth wizard" or wizard of the earth.

才国　[さいこく]　Kingdom of Sai
王采　[さいおう]　Royal Sai
中瑾　[ちゅうきん]　Chuu Kin, lit. "middle jewel," family name and given name of the Royal Sai
黄姑　[こうこ]　Kouko, lit. "golden mother-in-law," ruling name of the Royal Sai