A third plot idea is a time - travel fanfiction. Supergirl travels back in time and meets a younger version of herself. They have to work together to prevent a disaster that will change the future of her planet. This would involve a lot of character development as Supergirl has to confront her past self and the differences between who she was and who she has become.
Another plot could be set in an alternate universe where Supergirl lands in a world that has no concept of superheroes. She has to learn how to fit in while also trying to figure out how to use her powers without causing chaos. The fanfiction could explore her journey of self - discovery in this new world.
A plot could involve a time - travel scenario where Batman and Supergirl are sent back in time to prevent a major event that would change the future of both their worlds. They would have to work together, using their different skills and knowledge of their respective eras.
One idea could be a dark Supergirl who is corrupted by a powerful, evil force from outer space. She starts using her powers for her own gain, causing chaos in Metropolis. Another could be a Supergirl who has lost faith in humanity due to some great betrayal and turns to a darker path to 'teach' humans a lesson. And a third idea might be a Supergirl from an alternate, darker universe where her powers are more unstable and she has to constantly battle her inner demons.
Perhaps in the fanfiction, Supergirl is drawn to the Naruto world because of a strange energy signal similar to Kryptonite. Once there, she teams up with Sasuke who is initially distrustful but comes to respect her. They go on a quest to find the source of this energy. Along the way, Supergirl discovers that the energy is actually a by - product of an ancient and powerful jutsu. This jutsu was sealed away long ago, and now it's starting to leak, threatening both the Naruto world and potentially Supergirl's home planet if it spreads.
One plot idea could be that Superman and Supergirl team up to face a new, powerful alien threat that is immune to their normal powers. They have to rely on their wits and discover new abilities within themselves. Another could be a story where they travel to an alternate dimension where their roles are reversed. For example, Supergirl is the more well - known hero in that world and Superman has to learn from her.
One idea could be that Batman tries to train Supergirl to better control her powers in the context of the Injustice 2 universe. He might see her as a potential force for good against the tyrannical regime. Another could be that Supergirl discovers a way to bring back the more heroic Superman she once knew, and Batman has to decide whether to trust her plan or not.
One idea could be that Supergirl lands in the wizarding world by accident. She might be initially confused by the magic there, but her superpowers could also offer a new perspective on magic. For example, she could use her heat vision to enhance a spell or her super strength to protect Hogwarts from a new dark threat that the wizards alone can't handle.
In a fanfiction, there could be an alien race that is immune to Supergirl's powers but is vulnerable to the speed force. Flash discovers this during a battle where Supergirl is struggling. He then uses his speed to create a barrier around the aliens, trapping them long enough for Supergirl to figure out a new way to defeat them, like using her super - breath in a new way that Flash helps her direct with his speed.
Well, a great plot for Supergirl Arrow crossover fanfiction could be centered around a common enemy from another dimension. This enemy has technology that nullifies Supergirl's powers and Arrow's skills, so they have to rely on their wits and each other's unique strengths. For example, Supergirl could use her heat vision in a creative way to expose the enemy's weaknesses while Arrow uses his archery skills to set up distractions. They could also meet some interesting characters from the other dimension during their adventure.
One idea could be that a powerful villain creates a time - space rift that pulls both Supergirl and Flash into an alternate dimension where they have to team up to find a way back home. Their powers work differently in this new dimension, and they have to learn to adapt quickly.
One idea could be that Supergirl and Batman team up to stop a powerful alien weapon from being used on Earth. Maybe the weapon was stolen from a Kryptonian ship and Batman uses his detective skills to find clues while Supergirl uses her superpowers to fight off the bad guys who have the weapon.