One common theme is the power imbalance. With Eren as the king of titans and Levi being human, there's a natural power differential that authors like to explore.
Yes, there are. In many of these fanfictions, the authors explore the dynamic between Eren as the 'king of titans' and Levi in unique ways. They might delve into their power struggles, emotional connections, and how they interact with the human world around them. For example, some stories might have them working together to face a new threat in the world of Titans while also dealing with their own feelings for each other.
It's really hard to say. The Young Justice has some really powerful members like Superboy and Miss Martian. But the Titans also have strong characters like Starfire and Cyborg. It could depend on the situation. If it was a battle in an open field, the Titans' more experienced members might have an edge. But if it was a stealth mission - type battle, Young Justice's skills could give them the victory.
One idea could be a misunderstanding that leads to a battle between the two teams. Maybe a villain manipulates information so that the Young Justice team believes the Titans are up to no good. Then, as the fight unfolds, they start to realize they've been tricked.