Jyusya no Heki

From Fujoshi Bitches:

Seto works for a large corporation and has relocated to a desert kingdom to be in charge of infrastructure development. There, he meets the driving force of the project, Crown Prince Zia, a beautiful, good-humored and diligent member of the royal family. Goodwill develops between them as Seto works together with Zia, until one day, Zia suddenly goes, "Would you like to fuck me?" and turns up for a late-night romp...?! Bearing the responsibility of a country and a love that crosses social boundaries. Tarnished by gunpowder smoke and blood, a fairytale of a desert kingdom.