One plot idea could be that the Inhumans' city of Attilan is in danger and the Avengers are called in to help. The Inhumans are initially hesitant to accept their aid due to their differences, but they soon realize they need to work together. Another idea is a young Inhuman with a powerful but uncontrollable ability is found by the Avengers. They try to help the Inhuman learn to control it while also protecting them from those who would use their power for evil.
Black Bolt from the Inhumans would be really interesting. His power of destructive voice is so powerful that he has to be extremely cautious. In a fanfic, he could be the key to solving a major problem, but his inability to communicate easily (because of his power) could create a lot of tension and drama. The Avengers would have to learn to work around his unique situation.
One idea could be exploring what if Loki had an unexpected ally within the Avengers. Maybe a character who was initially on the heroes' side but got swayed by Loki's charm or promises.
One idea could be an imagine where a new superhero joins the Avengers. They have a unique power that the team initially struggles to understand but eventually learns to utilize effectively. For example, a hero with the power to manipulate time on a small scale, like being able to slow down time for a few seconds during a battle.
A more complex plot could involve the Flash's speed force interacting with the Infinity Stones. The Avengers might be trying to figure out how to use or contain the power of the speed force in relation to the Stones. This could lead to all kinds of conflicts and alliances within the story, as different characters have different ideas about how to handle such a powerful and unknown combination of forces.
Maybe a story where the Avengers are transported to Supergirl's universe. They have to adapt to her world's rules and help her fight against a powerful villain there. This could involve a lot of world - building and character development as the Avengers learn about Supergirl's allies and enemies.
A plot could revolve around the Avengers Prime traveling through time to prevent a future disaster that they somehow caused. Along the way, they meet different versions of themselves and have to make tough decisions about changing the timeline.
An Inhumans crossover fanfiction could involve a crossover with Doctor Strange. The magic of Doctor Strange's world and the Inhumans' abilities might clash or combine in unexpected ways. Maybe the Inhumans need Doctor Strange's help to deal with a magical threat that is affecting their city of Attilan. Or perhaps they can offer something in return, like a rare Inhuman artifact that has magical properties.
One idea could be that the Agents of Shield discover a new group of Inhumans with a unique power that could be a threat or an asset. They have to decide whether to help them control their powers or contain them. Another could be an Inhuman from the Inhumans group joins the Agents of Shield to help fight a common enemy, like a new alien threat. And a third idea is that some technology from Agents of Shield accidentally causes a power surge among the Inhumans, leading to chaos that both groups must work together to resolve.
A post - apocalyptic Inhumans setting where Medusa and Black Bolt have to fight to protect the remaining Inhumans. They could face new threats and challenges that test their relationship and leadership skills in a whole new way.
One idea could be that the next - generation Avengers have to face a new villain who has the power to manipulate time. They must travel through different eras to stop the villain from changing key events in history that would lead to the destruction of the world as they know it.