Kihanabou no Chouki Koi to En wa Utage Yori Hajimeyo

Sairin, whose status was lowered due to her late father's involvement in being arrested for treason, became the princess of Kihanabo. She tries to clear her father's name, but her purpose is discovered by the prince, Oren. However, he asks her for help in his revenge, and she ends up posing as his favorite concubine..? (Source: Kadokawa, translated)