12-ji no Kenryokusha

One day, Koyuki, a girl who works at a tavern in the port city of Salim, is saved from the advances of a feudal lord by a pair of twin princes, the cool and collected older brother Eleven and the free-spirited younger brother Twelve. After they invite her to the palace, Koyuki begins to learn the truth and destiny of the Empire. A royal fantasy revolving around the myths of the desert empire Orchis!!

(Source: Jmanga)