Arata: The Legend, Vol. 3 by Yuu Watase
In a mythical world where humans and gods co-exist, Arata has the unfortunate honor of being the successor to the matriarchal Hime Clan. This means he has to pretend to be a girl or face death if his true gender is discovered! Framed for the assassination of Princess Kikuri, Hinohara is sent to prison island Gatoya, where the fearsome warden Tsutsuga awaits him. Hinohara manages to escape his captors, and now he must make his way back to the Amawakuni capital. In order to get there, however, he has to first cross the region ruled by the treacherous Kannagi!