Flynn Scifo
Tales of Vesperia
"You know it's not our place to pass sentence on the crimes of others. He was to be punished in accordance with the laws!"
Flynn is one of Estelle's first and best friends, and very very important to her. He was the first person in her life to treat her like a person, not a title, and she spent a good deal of time with him in the castle. He told her about his life in the Lower Quarter, and about Yuri Lowell. Later, after Flynn left on his pilgrimage and Estelle learned of the plot against his life, she was determined to find him and warn him, despite the fact that she had never been outside the castle before, let alone outside the barrier.
Rita Mordio
Tales of Vesperia
"Having you pity me makes me want to jump off this cliff."
Despite Rita's surly demeanor, Estelle was determined to befriend her, and it certainly worked. Their personalities balance each other out very well, and they quickly become best friends over the course of the journey. Estelle admires Rita's confidence and magical abilities, and often tells her this. Rita, meanwhile, is pretty tsundere. AS USUAL.
Yuri Lowell
Tales of Vesperia
"I don't give a damn about your crazy ideas. We decide our own sense of what's right and wrong. The rest, I leave to my sword."
Estelle met Yuri while she was trying to escape the castle to help Flynn. He was the opposite of everyone she'd ever met - sarcastic, overconfident, and not afraid to announce when he thought the Empire was doing something wrong. He never allowed anyone to make his choices for him or tell him what to do, and Estelle quickly grew to admire this about him. He never forced her to do anything, and constantly encouraged her to make her own decisions, something that no one had ever done for her before. Yuri broadens Estelle's view of the world and changes her sense of right and wrong to an extent, and they are totally BFFs.