Kijoku: Princess Double Kari

After losing his mom to a mysterious death, Distol swore to himself that he will be the best swordsman in the world. However, his tragedy doesn't end there...Eight years after his mother's death, more bad news is brought to Distol. His sister, Princess Qoona, is chosen as the Holy Maiden. The Holy Maiden sacrifices her own life to give power to the seal that binds the demon king within. Normally, this would be a thing be proud of, but Distol does not want to lose another person he loves.
As Distol curses himself for not being able to protect the person that he loves, a witch appears out of nowhere and makes an offer to Distol. The offer is: "In return of giving great powers, you must invade Bastarauge, take the nation's treasure, kidnap Princess Elena, and corrupt her from within." A new dark age is about to begin...