Valentine is Ender's older sister, and she does what she can to protect him from Peter, their sadistic older brother. Valentine has much of Ender's compassion, but she does not have Peter's ruthlessness. However, as the story progresses, Valentine learns that the differences between the three siblings are not as great as they seem. She never ceases believing that Ender is the best of them, and she loves him unconditionally. In fact, her love helps save Ender when the pointlessness of Battle School threatens to break him. But as she begins working with Peter to transform the political system on earth, using her pseudonym Demosthenes, Valentine learns that there is a part of her that enjoys control.

Although she does not want to manipulate people for the sake of manipulation, like Peter does, Valentine knows that she is intelligent enough to make a major difference and sees no reason why she should not. However, she would never wish to do damage in her attempt to change the world. Valentine, like Ender, would never deliberately harm someone else. Unlike Ender, however, she falls prey to the irresistible urge to power. But that urge would never take her down Peter's road of power at any cost.