One interesting plot could be that they team up to fight a new and extremely powerful villain from another dimension. This villain has powers that neither Superman nor Supergirl has faced before, forcing them to combine their unique abilities in creative ways.
Another plot might be that Superman and Supergirl discover they have a long - lost relative who is also a Kryptonian. In the fanfiction, they embark on a journey to find this relative, which leads them to explore different parts of the universe and encounter various strange and wonderful civilizations along the way. This could also involve them learning more about their own Kryptonian heritage and powers.
Another plot twist might be that an alien force manipulates their DNA, causing them to swap powers temporarily. So Supergirl has Superman's classic powers like super - breath and Superman has to adjust to Supergirl's more heat - based vision and flight style. This would force them to rely on each other in new ways and learn from one another's experiences.
One interesting storyline could be Supergirl and Superman teaming up to face a powerful new villain from another dimension. They would have to combine their powers and learn to work in perfect sync to defeat this threat.
Well, obviously Superman and Supergirl are the most central characters. But other popular characters often include Lex Luthor. He is always a great antagonist, constantly devising new plans to take down the Kryptonians. His intelligence and deviousness add a lot of tension to the stories.
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 interesting plot could be that the Supergirl characters find themselves in the Supernatural universe. Maybe Kara has to deal with demons and angels while trying to find a way back to her own world. She could team up with Sam and Dean to fight a common enemy, like a powerful demon who has a vendetta against both the Supernatural world and Kryptonians.
Perhaps in the fanfiction, Batman is initially hesitant about his feelings for Supergirl because of their different powers and backgrounds. Supergirl, on the other hand, is more open and tries to break through Batman's tough exterior. Their romance could be a slow - burn one, with Supergirl using her kindness and strength to show Batman that they can be together, and they eventually fall in love while saving the world from a powerful alien threat.
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.
One interesting crossover could be the characters teaming up to fight a common supervillain. For example, Lex Luthor from Supergirl's world could team up with some of Arrow's villains like Deathstroke, and Team Arrow and Supergirl would have to combine their skills to take them down.
One idea could be that they team up to face a new and powerful villain from another dimension. This villain has the ability to nullify their powers temporarily, so they have to rely on their wits and non - superhuman skills. Another plot could be that they discover a long - lost Kryptonian artifact that holds the key to saving Earth from a natural disaster, but they have to solve a series of complex puzzles to unlock its power. Or perhaps they meet in a situation where they initially don't recognize each other as Superboy and Supergirl, and there's some humorous misunderstandings before they figure it out.
In this fanfiction, The Flash and Supergirl could start off as rivals. They both think their way of protecting people is the best. But as they face a common enemy that is too strong for either of them alone, they learn to work together and respect each other's abilities.