Koutei-tsuki Nyokan wa Hanayome toshite Nozomarechuu

Qatora was once a valiant knight of the Razanate Empire who gave her life to protect a young imperial noble. The tragedy cast her into the primordial Light of Origin, which not only revealed to her a dangerous secret... but also reincarnated her! She now lives as Lyse Winslette, the humble daughter of a poor baron in a neighboring country, who is doing everything in her power to keep her distance from the empire because of the forbidden knowledge she possesses. Lyse thus works her days away at the royal palace of Olwen as a lady-in-waiting. And she's rightfully mortified when she's chosen to attend the visiting Razanate emperor. Little does she know that she's about to learn another state secret that's going to land her... an engagement to an imperial knight?! She'll have to use all her skills—from this life and her last—to get out of this mess. Yet what is this strange feeling when she touches her fiancé's hand? Just who is Sidis, and what secrets is HE keeping? (Source: J-Novel Club)