Nikoli and Ayame have the highest ranks among the military. Law states there can only be two in that position.
The rest are highly ranked though are lower than Ayame and Nikoli, if that makes any sense.

Nikoli Haertel:

(I don't know where this is from only that it isn't mine so I can't take credit at all)

Ayame/Ekaterini Aldar:

Koemi Watanabe:

(I got lazy to colour her in so she has red hair and brown eyes, for the record).

Bianca Rinaldi:

Esbern Rinaldi:

Kilian Santaella:

(Baby boi he's only 19-)