Maiden Rose Series by Fusanosuke Inariya

Two soldiers caught on opposing sides of a war between nations must choose between country and an oath of fealty made long before. But the world that they live in is hard, distrustful, and cold. What will happen to their innocent love, as they are tangled ever deeper inside the terrible ravages of war?

Klaus von Wolfstadt, from one of the nations of the "Western Alliance," has left his duty as a soldier to his nation in order to be a knight to Taki Reizen, commander of the 15th division "Maiden Rose," whose country has an alliance with "Eurote," an enemy of the Western Alliance. The story follows their romance as it evolves from friendship, to love, and finally, to hatred!