Two outcasts in a warlock school discover one of them is a half-succubi when an ambitious familiar-summoning circle pulls one in.
The summoner outlogics the staff of the school who want to kill the half-breed (a breach of magical law) by positing that as his familiar and under his binding contract, she is his property assuming she's kept in check.
Now the two must work together to rise through to power and popularity, while trying to hold onto their identities.
Could have episodes of Demon-Student culture shock to both being a succubi and being female (ex. Succustudent has to start siphoning off others' body fluids to survive), cutthroat student politics, action involving magical combat, friendship and bonding while forced to spend time together, shared internal struggles as they resent the roles they need to fulfill to be an effective team (Summoner must be more dominant, Succubi must learn to be submissive)
A bigger lore arc involving his/her parents; the father is imprisoned for previously undisclosed crimes (Revealed to be siring with a demon), while the mother is missing.
Worldbuilding, such as introducing the Infernal Plane where demons reside unless they can get a contract with a human.