After Five Years of Substitute Marriage, I Became the Mightiest Witch

Selena strikes a deal with her twin sister, Aislin: she will marry the noble heir Kyle in her sister's place for five years in exchange for the "Inheritance Key," which will allow her to become a White Wizard. During the marriage, Selena endures the agonizing "Black Moon Curse" on Kyle's behalf, all while suffering constant humiliation and torment at the hands of Layla—Kyle's first love. Selena stoically tolerates this abuse to fulfill the five-year contract. Once the term expires, she successfully undergoes her magical transformation, and Aislin returns to take her place. However, Aislin’s odd behavior arouses suspicion; upon discovering the truth, a remorseful Kyle frantically searches for Selena. By this time, Selena has become a White Wizard and the Saintess of Lenseran, and has fallen in love with King Isone, a childhood acquaintance. Kyle repeatedly attempts to reconcile with Selena but is rejected; in a desperate move, he conspires to have Aislin impersonate Selena to deceive Isone, but the plot is exposed. Kyle’s crimes are revealed, and he is sentenced to death, while Selena—having endured so much—ultimately marries Isone.

World-building: Medieval European nobility (a setting where wizards and ordinary humans coexist).

Core Highlights: The heroine marries in her sister's place for five years solely to awaken her bloodline and become the most powerful wizard; by the time her ex-husband realizes his mistake and seeks to win her back, she has already become a revered Saintess.