Seikai no Monshou

Linn Jinto's life changes forever when the Humankind Empire Abh takes over his home planet of Martine without firing a single shot. He is soon sent off to study the Abh language and culture and to prepare himself for his future as a nobleman — a future he never dreamed of. Or wanted.

Now, Jinto is entering the next phase of his training, and he is about to meet his first Abh, the lovely Lafiel. But Jinto is about to learn that she is more than she appears to be. And together they will have to fight for their very lives.

[from AniDB]