A really interesting plot could be a time - traveling crossover. Supergirl goes back in time to the era of the original Avengers. She helps them in a battle that changes the course of history. In return, the Avengers help her find a way back to her own universe. During this time, she forms a special bond with Thor, as they both have superhuman strength and a connection to otherworldly powers.
Well, one possible plot could be that Supergirl accidentally lands in the Naruto universe. Naruto, being the curious and friendly ninja he is, approaches her. They initially have a misunderstanding due to their different worlds and powers, but then they realize they can learn from each other. Supergirl could teach Naruto about her advanced technology from her world, while Naruto could show Supergirl the unique chakra - based powers and the ninja way of life.
Well, it could be that Supergirl lands in the wizarding world somehow. Maybe she's chasing a bad guy who uses magic to escape to Hogwarts. And then she teams up with Harry Potter to fight the bad guy. Harry could teach her about magic while she teaches him about her superpowers.
One possible plot could be that the Supergirl characters find themselves in the world of Glee. Maybe Kara has to blend in at McKinley High while also dealing with her superpowers. She could join the glee club and use her super - hearing to help them perfect their harmonies. And she might have to face off against some villains who are after her while trying not to expose her true identity to her new friends in the glee club.
Perhaps in this fanfiction, Supergirl is accidentally sent to Lucifer's world. Lucifer, intrigued by her powers and pure heart, decides to help her get back to her own world. Along the way, they face various threats together and learn from each other's moral compasses.
Well, one possible plot could be that Supergirl is somehow transported to the Young Justice universe. Maybe there's a dimensional rift caused by some villain's experiment. She then teams up with the Young Justice team to stop this villain from causing more chaos across different dimensions. They could learn from each other's skills and powers along the way.
One possible plot could be that Supergirl, through some sort of inter - dimensional rift, ends up in the Star Wars universe. She might team up with the Rebel Alliance. Her superpowers would be a great asset against the Empire. For example, she could easily take down Imperial starships with her heat vision or super strength. Maybe she'd have to learn to use a lightsaber too, which would be an interesting addition to her powerset.
A 'Avengers Supergirl Crossover Fanfiction' might involve Supergirl's Kryptonian powers being a mystery to the Avengers at first. She could show off her super strength, heat vision, and flight, and the Avengers would be in awe. Then they'd start to strategize together. For example, Captain America would lead the group with his military tactics, while Supergirl uses her powers to do the heavy - hitting. And Hulk and Supergirl could have a fun interaction comparing their strength.
Well, perhaps in this fanfiction, there's a multiverse rift that pulls Nightwing into the Avengers' world. The Avengers initially mistake him for an enemy, but after some misunderstandings are cleared up, they realize his skills. Together, they face a new threat created by a combination of Hydra and some of Nightwing's rogues gallery who have also crossed over. Nightwing could teach the Avengers some stealth tactics while they show him how to handle more powerful cosmic threats.
One possible plot could be that the Shikon Jewel gets scattered across the Marvel universe. Inuyasha and his friends, like Kagome, have to team up with the Avengers to retrieve the pieces. Iron Man might be intrigued by Inuyasha's sword and try to study it, while Captain America could admire Inuyasha's fighting spirit. They'd face villains who also want the power of the Shikon Jewel, creating an epic adventure.
One possible plot could be that the Voltron team gets transported to the Avengers' universe. They might initially be seen as threats, but then they realize they need to team up to fight a common enemy, like a powerful alien force that's too much for either group alone. The Voltron lions could combine in the middle of New York City, creating an amazing spectacle.