One great storyline could be them facing a powerful new villain together. They combine their skills, Supergirl's superpowers and Alex's combat and strategic skills, to take on the threat. It shows their strong bond as sisters.
Supergirl might develop by learning to rely more on Alex's human - based skills and wisdom. For example, in a situation where her powers are nullified, she has to depend on Alex's combat training. Alex, on the other hand, could develop by becoming more confident in her role as Supergirl's support system.
One creative storyline could be a Supergirl from an alternate universe where she has different powers. For example, instead of super strength and flight, she has the power to manipulate time on a small scale. This could lead to interesting situations where she has to fix small time - related disasters in her city. Another could be a story where Supergirl teams up with an unexpected character, like a reformed super - villain from the DC universe, and they have to face a new, powerful threat together.
One great storyline could be where Supergirl and Lena Luthor have to team up against a common enemy that is threatening both National City and L - Corp. This forces them to put aside their differences and really understand each other on a deeper level. Another could be a time - travel story where they go back in time and see how their relationship could have developed differently. There are also stories where Lena discovers Supergirl's true identity in a very unexpected way and they have to deal with the fallout.
Well, it's hard to say who the 'best' is as it depends on personal taste. But some popular authors in this area might be those who have a deep understanding of the characters. For instance, some authors who have been writing for a long time and have a lot of followers. They are good at portraying Alex's strength and Maggie's charm in their stories.
One unique plotline could be that Alex's pregnancy gives her new superpowers. In some fanfics, this is a really interesting take as it shows how her body's change due to pregnancy might have unexpected consequences on her abilities. It adds a whole new dimension to her character.
One interesting story could be about them going on a mission together outside of National City. They face an unexpected enemy and have to rely on each other's skills. Alex uses her combat training and Maggie her detective skills to solve the mystery.
One interesting storyline could be a team - up against a powerful new villain that neither The Flash nor Supergirl can defeat alone. They have to combine their powers and strategies in a way they've never done before.
One interesting storyline could be a team - up where Supergirl and The Flash have to stop a powerful villain from another dimension. They use their combined powers of super - speed and super - strength to outwit the bad guy.
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.
One interesting storyline could be Kara adjusting to life on Earth as a young girl. Maybe she's trying to hide her powers while also making friends at school. Another could be her learning about her Kryptonian heritage in a more personal way, like finding a hidden family heirloom that gives her new insights.