The Doctor, who assumed the name Kenneth for his role, had created a holodeck program to experience family life. The first program was picture perfect, and Belle was the perfect daughter. She did well in school, never disagreed with her father and always got along with her brother. The second program set up by B'Elanna Torres allowed The Doctor to experience real family life. In this version, Belle became rebellious. She had to be told to clean her room and bordered on uncontrollable. Despite this, it was clear that she loved her father. Upon seeing how much her safety meant to him, she agreed to make a sacrifice, called him a good father, and gave him a hug, providing a tender moment.
One of Belle's sacrifices was going to Parrises squares on Tuesday, Thursday and Saturday, putting her on the second team. She protested at first, but eventually agreed. Belle later suffered an ultimately fatal accident at a Parrises squares match. The Doctor was so devastated as she asked whether she would be able to see again that he ended the program, unable to face that he could not do anything to save her.
Later, however, he opened up about the experience to Tom Paris after delivering a lecture to him, leading Paris to ask if he was alright. He admitted that he wasn't able to face what was happening and Paris encouraged him to complete the events of the program, noting that if he didn't, he would always be stuck at that point and miss the whole point of what it meant to be a family. With this in mind, The Doctor completed the program and provided comfort for his daughter as she died, as well as taking comfort in being there for her with the other members of his simulated family. (VOY: "Real Life")