Rianne Rasha is the only sister of Lady Yhelbruna, whom she calls Lea Rasha. She explained how she made a mistake in the past that separated her and her sister for centuries as leaders of the Hathran and Durthan. She became the Supreme Mother of the Durthan and along the campaign made a pact with Lauzoril that would give her back her rightful leadership over the Witches of Rashemen. The Durthan Plans found in her bedroom in session 3 already described her worry over the situation.
Along her life Rianne has never been fully evil. She made mistakes and had to pay for them, thereby taking a grim view of life that allowed her to close her heart to some of the things she had to do. In the end it was other high Durthan, like Lianne Kilarune that really made the Durthan evil. In the end she could not step down from her position as Supreme Mother for fear of what Lianne would do with the organisation and waited for her chance to change the organisation for the better. In the end a peace was made by her and her sister, after she helped the party destroy Lauzoril and Yuriath.
Although feared throughout the campaign, the party only met Rianne once and that was shortly after she saved their lives from Lianne. She explained her situation and offered to help take down Lauzoril, which she did. And then together with the party members talked with Lady Yhelbruna to set aside their differences and sign a lasting peace.