In addition to shaking his world-view, Keiki's encounters with the abnormal have led him to conclude that neither Sayuki nor Yuika are the elusive Cinderella. Through process of elimination, the only one remaining is Mao.
So that's why you two couldn't get along...
Ach, deshalb warst du so schroff zu ihr.
Por eso no se llevaban bien.
É por isso que vocês
não se davam bem...