Obviously, Peter is the main character. There could also be his neighbors who might play a role. For example, an old lady next door who gives him advice or a young boy who is curious about Peter's solitary life.
A great storyline could involve Peter deciding to learn a new skill like cooking. Since he lives alone, he has all the time to experiment. He might start with simple recipes and gradually progress to more complex ones. Along the way, he could share his food with his neighbors and form new relationships, which would be a big change for someone who lives alone.
In this fanfiction, Percy living alone could mean a whole new set of adventures. Maybe he's chosen to isolate himself after all the chaos in the demigod world. He could be exploring his powers in solitude, away from the distractions of Camp Half - Blood. It also might lead to some self - discovery as he doesn't have to rely on his friends all the time.
In some 'peter is alone fanfiction', he could be alone in a strange new place. For instance, he's transported to a different dimension where he doesn't know anyone. He has to adapt, survive, and maybe find a way back home all by himself. This kind of plot can explore his character growth, his resourcefulness, and how he deals with the isolation in a completely unfamiliar environment.
Perhaps Peter is alone in a forest, away from the city. He's there to find some peace and quiet, to get away from the chaos of New York. While he's alone, he reflects on his powers and how they've both blessed and cursed him. He might even start to train in new ways, using the seclusion of the forest to his advantage.
One common theme is self - discovery. Since Peter is alone, he often has to figure out his own strengths and weaknesses. Another is sacrifice. He might have to give up certain things to uphold his role as a hero.
There is indeed some. Some fanfiction might focus on Peter's internal struggles as a lone hero, like how he copes with isolation while still trying to do the right thing. It could also explore his relationships in a new light, given his solitary nature in these stories.
Peter might have an internal monologue about his loneliness. For example, he could be sitting in his room, staring at the ceiling, and thinking about how he can't really share his true self with anyone. He misses having a normal life where he doesn't have to constantly hide his identity.
Maybe the Vulture could make a comeback. In this fanfiction, he might be out of prison and looking for revenge on Peter. Or it could be a new villain that has heard about the young Spider - Man patrolling alone and sees it as an opportunity to take him down. And of course, there's always the possibility of Aunt May finding out more about his solo patrols and getting worried.