Pretty much all Negima cast (as it is heavily shounen) could be considered testaments to willpower. Yue's drive to become a Mage, to be like Negi, even when all things should suggest she quit. Well, it means the most obvious choice for any of them would be:



However, due to the character development after Yue's memory loss, the emotion that has been showing to be strongest, the connection her memories were rebuilding from. Her connection to a boy teacher, is love. Meaning that this also would work: