Isekai de Migawarihime Ninari Haou ni Ubawaremashita

One day, Serina, an ordinary woman, is suddenly transmigrated into the presence of Ceres Diana, the infamous princess of the Kingdom of Sipitria, notorious as a cruel and scheming vixen, with a face that looks just like Serina. Her kingdom is being attacked by the neighboring Heilbronn Empire. Serina is still confused by the situation when she is forced to take the place of the princess, and as the “princess” she is taken prisoner by Gilbert, the arrogant prince of the Heilbronn Empire. Now that Serina has fallen into the hands of the handsome but intimidating Gilbert, the fate that awaits her is whether she will become the prince's plaything, or......?

(Source: ComicWalker, translated)

Note: Chapter count includes two volume-bonus chapters.