I Met My Enemy at the Engagement Party

Two legendary sword clans are lifelong rivals. A former detective is reborn as the treasured daughter of one clan, only to be betrothed to the heir of the other to force a truce. At the engagement she meets someone tied to her past life, and the rival remembers that past as well. Jealousy from powerful allies turns the political match into a perilous, slow-burn enemies-to-lovers game. (Source: MangaUpdates, edited)