Quote Originally Posted by Andromeda
And then Momo is always Momo worrying about everything. How someone like her became a Vice-Captain I don't know.

Well, Momo is Himanori right? The 5th Division vice captain. The reason why she is a vice captain under Aizen is explained by Aizen himself.

Spoiler:
When still training, Hinamori, Renji & kira Izuru were to be assigned into Divisions. Aizen saw that Renji was the 'toughest case" of those three, so he got assigned into the 11th Division. Momo was the easiest to manipulate, especially since she idolized Aizen more than anyone. That way, she would easily help in their plans no matter what. They also used kira under Gin when he became a captain, for he was quite naive & obedient.


About her being a vice captain, other than it being Aizen's doing, her exceptional skills in Kidou are another factor determing that, even if the kidou attacks don't seem that strong when facing Hollows e.t.c.