A cool plot could be a time - travel crossover. Arrow gets sent to Supergirl's time or vice versa. They have to adapt to the different time periods and deal with threats that are unique to that era. For example, Arrow might struggle with the more advanced technology in Supergirl's time, while Supergirl has to learn how to fight without relying so much on her powers in Arrow's more grounded world.
One great storyline could be a villain that is causing chaos in both Arrow's Star City and Supergirl's National City. The two heroes team up, with Arrow using his combat skills and Supergirl using her superpowers to take on the baddie. They might initially have some differences in their approaches, but over time, they learn from each other and form a strong bond.
Another interesting idea is a mind - control situation. A powerful telepath takes control of some of the heroes and villains in their respective cities. Flash, Arrow, and Supergirl have to find a way to break the mind - control. They start by finding the source of the telepath's power. Along the way, they discover that the telepath has a tragic past that led to this misuse of power. They try to reason with the telepath while also fighting off the controlled allies and villains.
Another great storyline could involve a cross - dimensional rift that brings characters from Arrow's world into Supergirl's and vice versa. This would create a lot of chaos as the characters have to adapt to the different rules and environments. For example, Oliver might struggle with the presence of aliens in Supergirl's world, while Kara has to deal with the more gritty and crime - ridden Star City. It could also lead to some interesting character pair - ups and new friendships or rivalries.
One great storyline could be them teaming up to fight a common enemy like a powerful meta - human who is causing chaos in both of their cities. They could start off not trusting each other fully due to their different methods but then grow to respect one another as they see the value in each other's skills.
Perhaps a fanfiction where Supergirl arrives in Smallville during a time when Clark is struggling with his identity. She could be a source of inspiration for him, showing him the full potential of his powers. They could also have a friendly competition to see who can save more people in Smallville, which would be a fun and exciting plot.
One great storyline could be where Arrow and Batman team up to take on a common enemy like Ra's al Ghul. Arrow's skills with the bow and his street - level fighting ability combined with Batman's detective skills and high - tech gadgets would make for an exciting adventure. They could start off as rivals, not fully trusting each other, but as they face the challenges set by Ra's, they learn to work together and respect each other's methods.
A really cool story could be set in an alternate universe where Supergirl and Batman are the last two heroes left. They have to rely on each other completely and in the process, they discover new aspects of their powers and themselves. Their relationship could evolve from just being allies to something more complex and deep, with Supergirl teaching Batman to have more faith and Batman teaching Supergirl more about strategy.
To write a compelling character interaction, first understand the personalities of Arrow and Supergirl. Arrow is more brooding and street - smart, while Supergirl is optimistic and has strong moral values. Have them start off with a bit of a misunderstanding, like Arrow being suspicious of Supergirl's powers at first. Then, as they face challenges together, show how they gradually come to respect and rely on each other.
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 an alien threat emerges which requires the skills of both Arrow's team in Star City and Supergirl in National City. They have to combine their combat styles, with Arrow's more grounded and stealthy approach and Supergirl's super - powered attacks. For example, Arrow could use his trick arrows to create distractions while Supergirl takes on the stronger alien foes directly.
One idea could be that a powerful villain threatens both Star City and National City simultaneously. Arrow and his team are struggling with the more street - level threats in Star City, while Supergirl is dealing with the super - powered aspects in National City. Eventually, they cross paths when the villain's plan connects the two cities. For example, the villain might be using some sort of technology that is affecting the meta - humans in National City and also causing chaos in Star City's criminal underworld.