The protagonist Ruby is a black mage, a rarity in her country. In a world where white mages—saintesses—are treasured, black magic is treated as unknown, savage, and shunned by society. Even in that harsh environment, there was one person who seemed different: her half‑sister, the saintess Floria. Floria acknowledged black magic and always encouraged Ruby. But one day Ruby learns that this kindness was a lie. Egged on by Floria, Ruby had been using black magic “for the sake of the country,” only to discover it had actually been used for human experimentation without her knowledge. Branded with that crime, she is condemned. When Ruby comes to after her judgment, she finds herself several years in the past. In her first life, she was deceived, mocked for her black magic, and finally killed. In her second life, she vows: She will use black magic to protect the country from the saintess—and she will absolutely not die this time!! Having lived in loneliness, Ruby’s second life becomes something completely unexpected: people she never imagined begin to cherish her, and her black magic is transformed into a force for justice