Ness

Vanessa Danae, Cass's younger sister. Their parents had her once it was clear that Cass wasn't a summoner and therefore had no chance of becoming family head. She's perpetually angry about being a backup heir to him, especially since she can't match his natural charm or leadership skills, and the superficially nice way he treats her just makes things worse.

Just a regular teen in terrible and complicated circumstances, really.