Eternally Yours (Klaus X OC and Stefan X OC)

For Sadie Salvatore being immortal meant no more being abused by her father. After being forced to drink human blood by her younger brother, both Sadie and Stefan talked Damon into doing the same thing. After being turned her relationship with her siblings deteriorated badly. She stayed in touch with them, however, and spent time with Stefan in the 1920's before she returned to Carlisle and Esme. While with Stefan she met and fell in love with Klaus Mikealson -who could not compel her to forget him no matter how hard he tried. She stopped talking to both brothers after that since she promised to never reveal what happened during that time period. Almost a decade later her and Rosalie were out hunting when they smelled human blood. Both of them found and later saved the McCarty siblings. While Emmett became like the Cullen's, his younger sister became like Sadie. For the first time in 71 years she got her wish to have a child. She helped Callie get used to her new life and later gave Callie her own daylight ring. Sadie later returned home to Mystic Falls to check in on her brothers before she ended up returning to Forks to meet Edwards' human girlfriend.
For Calixta McCarty being immortal meant never having to lose her brother. While she was out camping with her brother they were both attacked by a bear. Rosalie and Sadie-who were out hunting found them and saved them. Calixta was in worse shape than her older brother causing Sadie to make a split second decision of changing Callie herself rather than trying to get her to Carlisle first. Callie dies with Sadie's blood in her system and wakes up later on in transitioning. Sadie told Callie that the choice was hers if she wanted to turn and that she had 24 hours to decide. Callie chose to go through with the transition and fed on a homeless man. After she was turned she used Sadie's old daylight ring until Sadie could get Callie one. She lives off of both animal and human blood most of the time much like her sire.