In an Arrow multiverse harem fanfiction, it could be that an ancient power source in the multiverse is unlocked. This power is connected to different female characters from various Arrow - inspired universes. The main character, who has a special connection to this power, has these female characters drawn to him as they all try to figure out how to control or use this newfound power for the greater good of their respective universes.
Perhaps the main character is a new hero in the Arrow multiverse. As he travels through different realities, he discovers that in each one, there are strong female characters who are intrigued by his unique abilities and his different take on heroism. They start to gather around him, creating a harem - like dynamic as they all try to help him understand and navigate the multiverse better.
One idea could be that the main character from the Arrow universe gets transported to different multiverse versions where he encounters various versions of female characters who are all attracted to him. They could form a sort of team to fight a common threat across the multiverse while also dealing with their complex relationships.
Well, obviously Oliver Queen from the Arrowverse could be the central male character. For the female characters, Felicity Smoak could be one from his own universe. Then from other multiverse versions, there could be a more ruthless version of Black Canary or a super - powered version of Laurel Lance. They could all interact with Oliver in different ways due to their different personalities and abilities from their respective universes.
Maybe in the fanfiction, the multiverse is collapsing and the Avengers of different universes are brought together by a mysterious force. They find out that an experiment gone wrong in one of the universes has caused this. So they have to travel through different universes, each with its own unique versions of the Avengers and villains. Along the way, they discover new powers and abilities that they can use to try and reverse the damage and save the multiverse.
Well, a cool plot for 'Avengers Multiverse Fanfiction' might be that in one multiverse, the Avengers are all villains and in another they are heroes as usual. The good Avengers from our known universe have to find a way to either convert or defeat their evil counterparts. Maybe there's a mysterious force that's causing this flip in morality across the multiverse and the Avengers need to stop it before it spreads further.
One idea could be exploring alternate versions of the main characters. For example, a version of Doctor Strange who turned to the dark side in another universe. Another plot could involve a love story between two characters from different universes that was not possible in the main MCU timeline. Or perhaps a story where the multiverse is collapsing and the characters have to find a way to stop it by traveling through various strange and dangerous universes.
Maybe there's a character who has the ability to traverse different universes freely in this 'the multiverse at war fanfiction'. Their journey to find a way to end the war by uniting the different versions of heroes from various universes would be really engaging. They might face challenges like different versions of the same villain trying to stop them.
Well, a plot could revolve around a young inventor in a parallel universe who discovers a way to communicate with the original Mega Man. Together, they try to find a solution to a virus that is spreading across multiple Mega Man universes, corrupting all the robotic beings. This would involve lots of action, as they have to fight their way through hordes of corrupted robots while also searching for a cure.
A great plot could involve the two heroes swapping cities for a while. Arrow tries to deal with Gotham's crime underworld while Batman goes to Starling City to investigate a series of strange disappearances that might be linked to a powerful criminal organization there. This would lead to both heroes having to adapt to different environments and crime - fighting styles.
Perhaps there could be a story where Lex Luthor somehow gets hold of some of Arrow's technology and Clark has to work with Oliver to retrieve it. They would have to combine their skills, Clark's superpowers and Oliver's archery and combat expertise.
Maybe there could be a crossover where the Flash accidentally travels to the Arrow's universe and they have to work together to get him back to his own world. Along the way, they discover a common enemy that has been operating in both universes.
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.