I think in my heart her magic is a mix of all magics.. she can summon far more than just what's limited in the game... she still has cross-class skills... lol
She excels in magics, but I think she might?? MIGHT do ok as a Sage. I think it suits her & makes sense lore wise. She CAN do astrologian readings but I don't see her ever using astro skills as its presented in the quests. She and Janne go way back. I also think it makes sense she'd know it because... Sharlayan & Ishgard :)
Her carbuncles name is Lemon.

Ruzha too, is a summoner! I think his fighting style is far more aggressive in general. He also is very good wish magic... I can see him as a reaper and as a dark knight pretty easily. But I think he is strictly magic unless he's backed into a corner. Ruzha has a hard time getting physically close to people (doesn't like being touched, needs physical distance from others) So I think he'd stick to mostly casters. He absolutely can fire a firearm though. Both bows and guns... He's got great aim!
His carbuncle doesn't have a name, it's just "Carbuncle", but he does love him. his little friend. his trusted creature. It's one of the only things Ruzha lets hang around closely to him at almost all times... probably because it's made of his own aether...?

Neither Sephine nor Ruzha actually need the summoners book at this point to channel magic. It's just a bit easier with a focus, and they're both strong, so holding a book to make things marginally easier is worth it. If the book is lost during combat though, it's no issue... Ruzha has 100% used the book to smash someone in the face when they got too close. I've talked about this before, I think, but I associate them both with fire in different forms... but either way, you see them with ifrit and phoenix pretty often. The bahamuts of course are also very common. Though usually in combat it's ifrit who comes out to play, unless it's serious...! Imagine if you will, someone who calls their summon out, and it STAYS out to fight, as it's own entity with the ability to communicate... Like that. Phoenix is more of a concept creation, and Bahamut doesn't speak. But the other primals they can call sure do chitchat. yappers.