Enemies to lovers

Assassin x Cinderella beginning, but without their undercover story

An assassin catches his spy, but they somehow end up married and she continues her mission to spy on him. He knows, but he adores her too much to stop her.

After growing up with a friendly rival in the academy for 10 yrs, the institution fell under attack. Both main characters were separated, and trained 10 more yrs to fulfill their revenges. Unfortunately, they were both on opposing sides of the war in Murin :(