The Assassin & The Mercenary

Howard Stark's sister (Elizabeth Stark) gets a crush on Bucky Barnes before he gets shipped to war. Lizzie follows along in order to help Howard, as well as government, with his efforts behind the curtain while also helping in any other ways she finds she can while on the front lines. Eventually she gets kidnapped by HYDRA and turned into the Winter Soldier's partner in crime. They both form a relationship of some kind while under the control of HYDRA. Eventually escaping and finding a new life as well as (eventually) each other.