Well, a possible plotline is that the Avengers see the Agents of Shield dealing with Inhumans. The Avengers, having their own views on super - powered individuals, could either offer help or be at odds with how the Agents handle the situation. Maybe they'd start training the Inhumans in a different way or try to relocate them. Also, there could be a plot where the Avengers watch as the Agents of Shield face off against Hydra within their own organization and then decide to step in and help root out the remaining Hydra agents.
In some of these fanfictions, the Avengers might watch the Agents of Shield during a time of crisis, like when a powerful alien weapon is discovered. The Avengers could comment on the Agents' strategies, and perhaps there would be a bit of friendly competition between the two groups in terms of who can solve the problem first. There could also be a focus on the relationships between specific characters. For instance, Tony Stark might be fascinated by Skye's hacking skills and offer to mentor her, which could lead to a whole new set of adventures and character development for both of them.
One interesting story could be about how the Avengers react to a particular mission in Agents of Shield that goes wrong. Maybe they step in to help and there are some great character interactions between the two groups.
Another great storyline could be about the Agents of Shield having to deal with the aftermath of an Avengers - level battle. They might be in charge of cleaning up, helping the survivors, and trying to figure out how to prevent such destruction in the future. This could show a different side of the Agents of Shield, as they are often in the background but play a crucial role in the overall Marvel universe.
Another storyline might be a time - travel plot where the agents go back in time to prevent a major event that would have led to the downfall of the Avengers. They could encounter younger versions of the heroes and change the course of history. This would involve a lot of character development and exploring different timelines.
One interesting storyline could be a crossover where Agents of Shield agents have to team up with the Avengers to stop a powerful alien threat that neither group could handle alone. This would involve a lot of character interactions, like Coulson trying to give orders to Iron Man or Natasha Romanoff teaching some of the Shield agents her spy skills.
One idea could be a story where the Agents of Shield team has to team up with some of the less - known Avengers to stop a new, powerful threat that is specifically targeting the more minor superheroes. This would give a chance to explore the dynamics between the two groups and shine a spotlight on the underrated characters.
One idea could be a crossover mission where the Agents of Shield team has to work with the Avengers to stop a powerful alien threat that is targeting both Earth and a hidden Inhuman settlement. The Agents could bring their espionage skills while the Avengers use their raw power.
A great fanfic idea could be about an old enemy from the Agents of Shield's past coming back and the Avengers being brought in to help. It could involve a lot of mystery, action, and the building of new relationships between the two groups.
In some fanfictions, the Avengers might watch the deaths in Endgame as a form of training or preparation for future battles. This could lead to them developing new strategies to avoid similar losses. For example, they might focus on improving their teamwork or finding new ways to protect each other. They could also be haunted by the deaths they saw, which could affect their mental state during subsequent missions.
One common plotline is the Avengers reacting to alternate versions of the Civil War events. For example, they might see a version where more heroes died during the battle. Another is them getting to interact with the characters from the Civil War in a different setting, like a post - apocalyptic world where the events of Civil War led to total chaos.
One idea could be that the Agents of Shield discover a hidden threat that is related to an old Avengers enemy. For example, a Hydra remnant has found a way to re - activate some of the technology left behind by Ultron. The Agents of Shield then have to team up with the Avengers to stop this new threat. They could combine their skills, like the Agents' espionage and the Avengers' super - powers.