There aren't that many secondary characters, but they can be summarized as Leigion CVII and the Beasts
Beasts
This group includes people such as: Spartan, the ability to electricute; Gaurdian, the giant spirit that practicaly made sure Atrocity stayed alive; and of course the piston, the loyal gaurd that makes sure that Atrocity stays alive.
Lightly57
The group of people here have a bit more of a connection outside of KYRA, a couple include: Val, the loyal friend and expert in medical care; Brooklynn, Sister and great archer; and Fortin, the teacher and mentor to Lightly57