One idea could be that Captain Marvel and Spider - Man team up to stop a powerful alien threat that's immune to most of Earth's defenses. They'd have to combine their unique powers. Captain Marvel's energy - based attacks and flight, along with Spider - Man's agility and web - slinging skills, would make for an exciting battle.
Perhaps there's a situation where an evil scientist creates a device that can disrupt super - powers, but it has an unexpected side - effect that also links the minds of Captain Marvel and Spider - Man. So they have to work together while also dealing with sharing thoughts and emotions, which could lead to some comical and heart - warming moments.
A possible plot could be that a new villain emerges who has the ability to manipulate time. This villain sends Spider - Man back in time to a point where Captain Marvel was just starting out as a hero. Together, they have to find a way to get Spider - Man back to his own time while also preventing the villain from changing history in a disastrous way.
Another fanfiction concept could be a mentorship situation. Spider - Man looks up to Captain Marvel as a powerful and experienced hero. She could train him to better control his powers and also teach him how to handle the pressure of being a hero on a larger scale. This could involve some intense training sessions where Spider - Man has to push his limits, and Captain Marvel shares stories from her own experiences in the galaxy.
Another plot could be that Spider - Man loses his memory and has to rediscover who he is while still trying to protect the city. This would put him in a vulnerable position and force him to rely on his friends and allies in new ways.
Maybe in the fanfic, Captain Universe's power has a mind of its own and it tries to take over Spider - Man. Spider - Man then has to fight against this internal struggle as well as external threats. This could lead to some really intense character - development moments.
Maybe a plot where Spider - Man has to face an alien invasion in the context of the 2017 cartoon. The aliens could have unique powers that his usual foes don't, forcing him to adapt his fighting style. He might also have to team up with some of his rogues' gallery who are also threatened by the invasion. This would create an interesting dynamic as they have to put aside their differences to save the city and the world.
Imagine in the fanfiction, Spider - Man discovers a new ability during Endgame that can complement Captain Marvel's power. He shares this with her, and they experiment with combining their powers in new ways. For instance, Spider - Man could create a web - like energy field using his new ability, and Captain Marvel could charge it with her cosmic energy to create a powerful shield or weapon against the enemy.
The plot might involve an interdimensional force that accidentally merges the worlds of Spider - Man and Captain Marvel in a way that forces them into a shared adventure. They could be in a situation where they have to protect a group of innocent people caught in this strange merge. Since they are from different hero backgrounds, they initially clash but then gradually learn to work together as they face greater threats.
A plot idea could be that Spider - Man discovers a hidden agenda of one of the sides during the civil war. He then has to decide whether to expose it or keep it to himself, as it could have far - reaching consequences for the superhero community.
One idea could be to explore what would happen if Spider - Man had to team up with his greatest enemies to face an even greater threat. For example, teaming up with Doctor Octopus and Green Goblin against an alien invasion. This would create a lot of interesting character dynamics as they have to put aside their differences.
One idea could be Captain Marvel bringing back some alien tech that the Avengers have to figure out how to use. It could lead to new powers for some of the members or a new way to defend Earth.
Maybe in the fanfiction, Spider - Gwen gets lost in the future where Spider - Man 2099 exists. He has to help her get back to her own time while also protecting his own version of New York from the chaos her presence might bring. They could learn from each other's fighting styles and develop a unique bond in the process.