Jibril

Jibril (ジブリール) is the youngest and strongest of the Flügel race. Her love toward knowledge starts even before the declaration of the Ten Oaths. She is against the book sharing law, and left her homeland to win the main library of the human world from the previous king in a game. When Sora heard what happened to the library, he challenges Jibril so he can gain knowledge of the other kingdoms. When she loses the game, she becomes Sora and Shiro's servant since she bet herself. After watching her personality during the game for nearly an entire day, Sora grasped her personality and a way to defeat her. Jibril thus takes Sora as her master. Over time she begins to understand and accept Sora's belief in the potential of humans. Unlike Steph, Jibril is happy to become the siblings' underling, and is shown growing feelings toward Sora.

Trivia
Jibril is an Arabic variant of  Gabriel.