Seikai no Monshou

The story follows Jinto, whose world was taken over by the largest empire in the galaxy: the Abh. Jinto's father, the planet's prime minister, handed their world over to the Abh in exchange for a standing in the Abh Empire. As a result, Jinto became a prince and was shipped off for an Abh Education. There he meets a princess of the Abh Empire, Lafiel, whom he quickly befriends despite her cold exterior. The Abh Empire is plunged into war soon after and the story continues from there...

(Source: Anime News Network)

Note: The last episode aired with a runtime of ~40 minutes as opposed to the standard 24 minute long episode.