WMG / Violinist of Hameln

Sizer is the fifth hope.

The Five Hopes are gushed about over and over again about the saviors of humanity, Oboe is a full-blooded Mazoku who has already been alive for at least hundreds of years and so it seems odd for him to be one of the chosen ones. On the other hand, Sizer is the twin sister of the chosen one, a direct descendant of the original hero, of the same age as the rest of the party and has considerably more relevance to the story. Oboe was never one of the Five Hopes, just a mentor figure. This is never confirmed in the series, but makes more than enough sense.