[quote=@Daxam]
I just realized I turned Zac into a summon
[/quote]

More like in KH2 when Mickey would randomly show up when Sora was beaten sometimes and you could play as him. 

I imagine summons working different depending on the character calling them. Lkke a White Mage character would have more like an FFX summon that steps in and acts as their offensive measure. 

For a more combat focused mage they could be more like FFXV where they're the pinnacle of offensive magic embodying the purest form of their element and just completely wreck things with one blow. 

Hoshi would likely have more of a support oriented set of summons. Matbe something akin to Ansem's guardian in KH1? Although I think we could also have our characters specialize in different KH mechanics. Like, one character runs the table on Drive Forms, another discovers how to use form change on their Keyblade, etc. Something to make everyone unique in what they bring to the table. 

So far as the main quintet goes, I'd personally pin the following: 

Alias. The Riku. Impecable synergy with his inner Darkness. Uniquely capable of traversing Dark Corridors and the RoD. 

Hoshi. Dual-Wielder. Considering planned story arc, she'd individually able to dual wield Keyblades without use if Drives. Might come up with some builds for different Key combos. To think of it, Form Changes could also lump into this to make her more of a Keyblade Technician. 

Levi. Drive Guy. Just strikes me as the one that can get on with everyone. Drives tend to be fueled by the bonds characters have with each other?

Lucian. Summon Guru. As a Prince of Heart he has a special connection to the worlds and their peoples. The Hearts/Souls of those from worlds lost to Darkness could find a safe haven with him, and come to his aid in combat. 

Morgan. Master Mage. Access to tiers of magic higher than the 3rd level "ga" spells. Can become capable of casting multiple spells AT THE SAME TIME! And mixing/blending elements?