Black Widow is another popular character. Her skills as a spy and fighter make her a great addition to any crossover fanfiction. She could be involved in a mission with the Guardians where she has to use her stealth and intelligence to outwit their enemies. Also, her complex backstory gives writers a lot to work with when creating new storylines.
One interesting fanfiction could be about the Guardians and Avengers teaming up to face a new, powerful villain from another dimension. In this story, the different personalities, like Star - Lord's charm and Captain America's leadership, would clash and then blend as they figure out how to defeat the enemy.
Well, there could be a huge battle against a common enemy. Maybe Thanos is back again and the combined forces of the Avengers and the Guardians have to use their unique skills to defeat him. For example, Iron Man could team up with Star - Lord to come up with a high - tech plan, while Thor and Drax could be on the front line, using their brute strength.
One exciting plot could be that the Guardians and the Avengers have to team up to stop a powerful cosmic villain who is collecting powerful artifacts from both Earth and other planets in the galaxy. The Guardians' knowledge of the galaxy and the Avengers' understanding of Earth could be combined to track down the villain.
One exciting plot twist could be that the Infinity Stones have a different origin in this fanfic. Maybe they were created by an ancient race that both the Avengers and Guardians have to discover together. This would force them to work closely and share their knowledge.
Black Widow and Nebula would make for an interesting pair too. Both are strong female characters who have had a rough past. They could bond over their experiences of being in the shadow of more powerful male figures in their respective groups. And they could also team up to take on some of the more dangerous enemies, using their stealth and combat skills.
One idea could be that the Infinity Stones are scattered across different planets again. The Avengers and the Guardians have to team up to find them before a new villain does. Maybe Thanos has a long - lost relative who is out for revenge and wants to use the Stones' power for destruction.