I think Nanaka falls under, Domination/Zoner.
She's about keeping herself at a distance while barraging with very High powered magic to keep them from getting in combat range, cuz once you get close, her options begin to dwindle, being weak to physical (Specifically Bash and Gun).
Symphonia Magic is by nature, versatile. You can cast damaging spells, Terraform, use it to buff yourself, use it to hinder opponents, place traps, and so on. So for someone who needs to play Keep a way, It has plenty of options.
Shinji on the other hand is more a All Around or Dynamic character? Mostly due to the way he uses Symphonian magic less as a weapon, and more as an advantage. He prefers to play Zoner and snipe from a distance, but due to being more durable than Nanaka, Enemies expecting him to fall to being in CQC range will be surprised. He's perfectly capable of fighting in close combat or at a range, He's not a tank, but he's not frail. His magic is versatile so he has an out for almost every situation he finds himself in (Warping helps a little :p ).
Stella..... I'm not sure what style she stands under. Gimmick probably, She only has a set amount of skills, Most of which are long range, but she has no real "Zone Control" Skills. Plus she has that cool-down mechanic which would be really hard to handle. So I think she'd fit under "Gimmick/Strong but Difficult" Category.
Ah, Almost forgot Kotori. Rushdown Domination. She attacks, she attacks, she infuses and then she attacks again, when she needs to defend she attacks, when she needs to dodge, she dodges then attacks. She's decently frail if not for magically reinforcing her body, and she doesn't have any high powered magic, she's pure CQC with a few small Mid range attack options, so she needs that battle to end as fast as she can end it.
(edited by Akamoto_Nanaka)