MangaDex

The Beloved Saint is Trying to Save the Villain Who has Fallen into Darkness.

Lacking magical powers, Sphere, the daughter of an earl, has been confined to her mansion since she was a child. When her stepmother and stepsister arrive after her father remarries, she realizes she has been reincarnated as the heroine of an otome game. She immediately uses her knowledge of games to acquire the powers of a saint and enrolls in the magic school where the game is set. Her goal is to be united with Ewald, one of the characters she loved even before her reincarnation. She then goes on to save the villainous character who has fallen into darkness and find happiness. (Source: Kadokawa, translated)