I think it should be about starfire as each one has had it's own subplot for a titan story arc. I have two ideas 1. It could be about starfire trying to find her long lost brother darkfire 2. It could exploring starfire being unable to relate to humans. Here me out this idea is based on a comic I read about starfire dating this sabitoire Robbie Reed who worked for the H.I.V.E which in the comics was a terrorist group in purple robes. The teen was hired to mess with and eliminate starfire, but both fell in love with each other. In my story arc both characters are kept but, the H.I.V.E turns out to be more than a school for villains and area larger group that was just funding brother blood. Along with several other teen titans villains like Mad Modd, Dr. Light, and have plans world conquest. They decide to target the titans through starfire and play on her insecurities with the help of Robbie who shows up makes her question her relationship with the titans and Robin. So that he can trick her into helping the H.I.V.E take over. Robin finds out and has to work to get Starfire back from this guy and the H.I.V.E.