Seijo no Ane desu ga, Naze ka Miwaku no Koushaku-sama ni Tsukaeru Koto ni narimashita

The life of Floria, the daughter of a poor baroness, has been drastically changed by an oracle. Her sister Renata, who was supposed to be shy, changes her attitude after being chosen as a saint, and for some reason she begins to see Floria as an enemy.
In order to escape from Renata, Floria is sent to work as a servant in a nobleman's mansion, where she meets the most beautiful duke, Desiree.
Floria's daily life changes dramatically and vividly after meeting him.