Sounds like Mystique would make a very interesting love interest for Null, considering her relationship with Rogue and Kurt, as well being a villain to the X-Men. And, as already mentioned, at some point, Null would be able to shut down her shape-shifting abilities to expose her true self. Unless there is a change in locale, or she masquerades as a student or teacher at the school carefully, she wouldn't be around Null enough to develop into one of the three love interests that each chapter will have. Perhaps, she'll have to be a DLC character who becomes curious about him given his new relationship with Rogue (and perhaps his accomplishments on the team if the story has progressed enough), then takes a personal interest in him after she gets better acquainted with him and his abilities, which then becomes a brief (and secret) sexual relationship (like a booty call?).