Aiko Mimura is the central character, originally a male soldier betrayed and killed during the Crusades. Vowing vengeance, he was reincarnated as a woman. Reborn as Aiko, she rises to become a military leader who unites the world and abolishes all religion. Haunted by past-life memories, she travels back in time to prevent the death of her lover Daisuke during the World Restoration she herself orchestrated. Her mission requires her to kill the Christian Crusader Hans, destined to be reincarnated as her, creating a paradoxical conflict. Throughout her journey, she is pursued by the Female Crusaders of St. Michaela's College, forces she once commanded. The name "Rika" does not appear as a character within the available information about "Sins of the Sisters".