Kyuutei Nyokan Myeong-hwa: Taiyoukyuu no Kage to Unmei no Ouhi

Myeong-hwa, a court lady, tries to get ahead in life, but is seen as an enemy by her superiors. However, her life turns around when she meets a young, attractive military officer in the palace and is offered a strange deal. The next morning, Mweong-hwa is ordered to be a candidate to become the king's concubine!

(Source: Kadokawa, translated)