Cordelia

Cordelia was the daughter of a Demon Lord and is Karlheinz's first wife, as well as the mother of the triplets named Ayato, Kanato and Laito. Prior to the start of the series, she was killed by her sons, but Richter removed her heart and had it transplanted into Yui so she would be able to resurrect in a different body. Cordelia also despises Karlheinz's second wife, Beatrix, since she was the first to conceive children instead of her. She tried to make her sons look better than Beatrix's by pushing her oldest triplet Ayato to always be the best in an unloving way. In the anime, when the 'awakening' occurs, she possesses Yui and attempts to annilihate the Sakamaki brothers with Richter's help which backfires when Richter reveals that he never loved her from the very beginning. In the final episode of the anime, Cordelia is finally destroyed and permanently removed from Yui's body.