Dress na Boku ga Yangotonaki Katagata no Katei Kyoushi-sama na Ken

An ordinary boy called Sherlock Doyle is captured and forced to put on his twin sister's dress by the Emperor's diplomat to be shipped to a small country called Ehren. His genius sister, Glinda, went missing two days before she's supposed to be sent to Ehren to be an royal tutor for the King's children. The sudden life change is too overwhelming for Sherlock, but he sees no way out. Later, he finds out the disturbing truth about the kingdom's intention with his sister.

(Source: MU)