A possible plotline could also be Naruto's struggle with loneliness and how he overcomes it. He might start writing letters to his friends (even if he doesn't send them) as a way to express his feelings, and through this, he gains a better understanding of himself.
One possible plotline could be Harry exploring his magical abilities in solitude. He might discover new spells or magical artifacts that he keeps to himself. Another could be him building a secret sanctuary where he can retreat from the wizarding world's chaos.
One possible plotline could be Sarutobi mentoring Naruto more closely. Since he's alive, he could pass on even more of his wisdom and jutsu knowledge to Naruto. For example, he might teach Naruto some of the more secretive fire - style jutsu that only he knows.
One possible plotline could be Kushina getting to train Naruto personally. Since she was a powerful kunoichi, she could pass on her unique skills and knowledge. This would make Naruto even more formidable at an earlier stage. Another plotline might involve Kushina's influence on Naruto's relationships. For example, she could have a big impact on how Naruto interacts with Sasuke, perhaps helping to prevent some of the rifts that occurred between them in the original story.
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.
There might be a fanfiction where Kotaro goes on a small adventure in the park near his house. He discovers a hidden spot that he decides to make his own little secret place. He could bring some of his things there and decorate it in his own unique way, like using stones and twigs to create a small boundary.
One interesting plotline could be Harry learning the pure - blood traditions from the Malfoys in a different way than he expected. He might gain a new perspective on the wizarding world's social hierarchy.
One possible plotline could be Harry trying to hide his wizarding past from his muggle friends and coworkers. For example, he might accidentally use magic in a moment of panic and then have to cover it up.
A great plotline would be if Jessica came back as a sort of supernatural being herself. Maybe she was brought back by a powerful witch, but not fully human. This would create a whole new dynamic as Sam would have to deal with her new state. She could be on a quest to find out who brought her back and why, and in the process, she and Sam could rekindle their relationship in a very different way compared to before.
Another plotline might involve Shmi becoming a key figure in the Jedi Council's decisions. Since she has a unique connection to Anakin, she could offer insights that the Jedi had overlooked. This could lead to a whole new set of alliances and power dynamics within the Star Wars universe.
One interesting plotline could be them sharing a flat in London after the war. They support each other through their post - Hogwarts careers, Hermione in the Ministry perhaps, and Harry as an Auror. There are little domestic moments like cooking together or discussing the latest wizarding news over breakfast.