Guinivere is a major non-playable ally from Fire Emblem: The Binding Blade and a minor non-playable character from Fire Emblem: The Blazing Blade. She is the half-sister of Zephiel and the princess of Bern. In Fire Emblem: The Blazing Blade, it is stated that her mother was King Desmond's mistress. She went to Roy for help when she saw that Zephiel had gone too far. Unlike her older brother, she does not want a war to happen, and she still remembers how well they got along as children, before King Desmond attempted to kill Zephiel.
Together with her lady-in-waiting, the cleric Elen, Princess Guinivere joins Roy early in the game in an effort to stop Zephiel. Eventually, she becomes the queen of Bern after Zephiel's defeat, despite the protests of some aristocrats.
Guinivere is usable on the trial maps of Fire Emblem: The Binding Blade once the player has completed the game nine times, and one of them in hard mode.