There's two playable Protagonists in Adventure High: Dan and Rosa.
Dan/Rosa is a childhood friend of Valerie, or Val for short.
While they share most of the same spells, one is exclusive to Dan at present time.
The Protagonist currently has 10 spells as Rosa and 11 as Dan.
Sarah is only datable if you're playing as Dan. As such, you can only access the Bubble spell as Dan.
Rosa currently has no female-exclusive relationships.
While a normally calm person, it's up to the player to decide how the Protagonist is in the end: Either a caring person who wants to stop Drape from abusing his power to change school to his fitting, or enslave everyone in the school. Or, hell, cause everyone in the school to turn into bimbos (Mass Bimbofication Ending).