Seijo no Soshitsu ga Nai node, Last Boss wo Mezasu Koto ni Shimashita

Rina Amakusa is exhausted from her job at a black company. Her only refuge is her favorite otome game. "I want to become a saintess too." Suddenly, Rina is summoned into the game with the body of the protagonist, but things don't go as expected. Thousands of attempts to save the world are met with brutal betrayals at every turn by everyone; her friends and family, her comrades, even the king and the people. The world she loved and the characters she adored are rotten to the core. Rina has had enough. Only revenge remains as the saintess becomes the final boss.