I Became a Concubine, but You Don't Have to Love Her, Right? ~The Other-Dependent Concubine Wants to Live a Lazy Life~

Barbara is chosen to become the fourth concubine of King Dorgan, as he is yet to be blessed with children. She devotes herself to King Dorgan and Queen Evangeline and goes out of her way to help them in order to secure a comfortable retirement for herself. The plan: Survive in the royal palace, where intrigue is rife!

https://www.cmoa.jp/title/338575/