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.
Another idea is that there is a cosmic entity that mistakes Spider - Man for Captain Universe and endows him with the powers. Spider - Man has to prove himself worthy of these powers and at the same time figure out why he was chosen, all while using the powers in his own unique way to protect the city.
One interesting aspect could be the unique powers Spider - Man gains as Captain Universe. It makes for really cool action scenes. For example, his strength and agility could be enhanced to an even greater degree than his normal powers. Another aspect is how his character might change in the fanfic. Maybe he becomes more self - assured or takes on more global - scale threats.
Some fanfictions focus on the origin of Captain Universe Spider - Man. They might explore how Peter Parker gets chosen to be the host of the Captain Universe power. It could be a story full of mystery and unexpected events, like a hidden prophecy or a special connection between Peter and the cosmic forces that leads to him obtaining these powers.
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.
Obviously, Spider - Man is one of the main characters. He's the one who gets the Captain Universe powers. And Mary Jane Watson might also be a main character as she's an important part of Spider - Man's life. Another could be J. Jonah Jameson, who always has an interesting take on Spider - Man's activities, especially when he becomes this more powerful version.
One idea could be Spider - Man teaming up with a new, original superhero created just for the fanfic. They could face a villain who has the power to manipulate time, causing chaos in New York. Another could be exploring what would happen if Spider - Man lost his powers temporarily and had to rely on his wits and the help of his friends to stop a crime wave.
Another plot could focus on a young Gwen Stacy from a different universe who stumbles into the main Spider - Verse. She has to learn how to control her powers while also dealing with the fact that in some universes, her counterpart didn't survive. This would add an emotional depth to the story as she tries to find her place and make a difference.
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.
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.
One idea could be that Spider - Man gets accidentally transported to the DC universe. He teams up with Batman to take on a common enemy like the Joker who has somehow gotten his hands on some Oscorp tech. They combine their detective skills and combat abilities to stop the chaos.
Maybe Spider - Man discovers a new threat that the Avengers have overlooked. He then tries to convince them of the danger, facing skepticism at first but eventually winning them over with his tenacity and evidence. For example, he could find a hidden group of villains planning to use a new type of technology to take over the world.