No date announced yet. The teaser visual was posted alongside the announcement on the publisher’s official twitter account. Synopsis from MAL for the manga adaptation:

Rising from the ashes, a fallen noblewoman stands to save humanity!

“Countess Romelia. I’m breaking off our engagement,” declared Prince Henri, right after defeating the Demon King. By the prince’s side were Saint Elizabeth, the sage Ekaterina of the Unreturning Forest, and the Eastern swordswoman Lu Hime, all pointing accusatory fingers at her as “useless.” But the prince and his comrades didn’t know something. They didn’t know that Romelia possessed a miraculous power called “Grace,” which bestows good luck.

Having lost her fiancé and been abandoned by her friends, Romelia did not break. Her homeland was still infested with the Demon King’s forces, and many people were held captive by the demon race as slaves. To rescue them, Romelia embarked on a mission, encountering numerous difficulties along the way. First, she didn’t have an army. There were no healers to tend to injuries, and she lacked the funds. But Romelia was determined to solve every problem aggressively.

• “No army? Let’s intimidate local lords and take their forts.”
• “No healers? Let’s negotiate with the church for their assistance.”
• “No money? Let’s negotiate with merchants to secure funds.”
• “Newly recruited soldiers are inexperienced? Let’s have them gain experience by hunting monsters.”

And so, Romelia, along with her loyal followers, marches into battle!