Akuyaku Reijou ni Tensei Shita Inaka Musume ga Bad End Kaihi ni Idomu Hanashi - Shinitakunai no de Last Boss Yori Tsuyoku Natte Mita

A girl living in the countryside is attacked by a monster and meets an unexpected death. When she wakes up, she has been reborn as the villainess in the story of her favorite book! In order to avoid a life of "certain doom" in which she will be killed by the Demon King as the enemy of the heroine, she acquires the strongest power, but ends up embarking on an unknown route in which the Demon King proposes to her...!? Armed with knowledge of the story and the strongest power, she challenges the bad ending, and a great reversal fantasy begins!

(Source: Manga UP!, translated)