Essentially each of these characters (Karai, Jennika, Fugitoid, Venus) are all the biggest supporters/Sufferers of the big bad evil guys (Shredder, Purple Dragons, Kraang, Big Mama). They're the main dudes that the turtles fight for and save from the villains even though they kinda started out as villains themselves, they were just trapped in their circumstances.
I like to imagine in some type of imaginary sequel movie of my version of tmnt's imaginary tv series (yeah those words make sense when reading them /s) they're the one's who defeat the big bads once and for all. So they kinda make like, a sequel team. So I tried to play around and balance out their personalities and team dynamics!