The male SI could be a former Shinra soldier who defected. He has insider knowledge of Shinra's operations and uses this to help Avalanche in a more strategic way. He could also have a special ability like being able to communicate with the Planet on a deeper level than most characters. This allows him to understand the true nature of the threat Sephiroth poses and helps him convince others to join the fight against Sephiroth in a more unified way.
One idea could be a male self - insert who has the power to control time. He uses this power to prevent certain tragic events in the Final Fantasy 7 world, like the destruction of Aerith. Another plot could involve the male SI being a master of a new type of materia that no one has seen before, which attracts the attention of both Shinra and Avalanche. He has to decide which side to ally with or if he should remain neutral.
One idea could be exploring the backstories of the minor characters in more depth. For example, the story of the civilians in Cocoon who were affected by the events. Another could be a what - if scenario, like what if Lightning had made different choices at certain key moments. And a third could be focusing on the relationship between Fang and Vanille before they became l'Cie.
A great plot idea could be an OC that is a former villain who has seen the error of their ways. They now try to redeem themselves by helping the heroes. For example, they might have insider knowledge about the plans of the main antagonist. Another plot could be an OC who is a healer with a very unorthodox method of healing. They are initially scorned by the traditional healers but prove their worth during a major battle. Also, an OC who is a thief with a heart of gold, stealing from the corrupt nobles to help the poor and then getting involved in the main story's quest could make for an exciting fanfiction.
One idea could be exploring the backstories of the minor characters. For example, the SeeD trainees who don't get much spotlight in the game. Another could be a 'what if' scenario, like what if Squall and Rinoa didn't end up together? It could also be interesting to write about the world of Final Fantasy 8 from the perspective of an ordinary citizen living in one of the cities, dealing with the sorceress wars and the chaos that ensues.
One idea could be exploring the backstory of the main character's family in more detail. Maybe there were secrets or hidden powers within the family that were never fully explored in the game.
A possible plot is that Fem Harry is a hybrid of a human and a Final Fantasy creature. This makes her an outcast in both worlds. She then embarks on a journey to find a place where she truly belongs. Along the way, she meets a group of rebels in the Final Fantasy world who are fighting against an oppressive regime. Her skills and courage make her a valuable asset to the group, and together they strive to change the world for the better.
One plot idea could be that Naruto is somehow transported to the world of Final Fantasy 13. There, he meets the characters and due to his unique abilities and charm, a harem starts to form around him. He could use his ninja skills to help the characters in their battles against the fal'Cie. Another idea is that the characters from Final Fantasy 13 are brought to the Naruto world. The different cultures and powers collide, and as the FF13 characters adjust, they are drawn to Naruto, creating a harem situation. The harem members could then team up with Naruto to protect both worlds from common threats.
One idea could be a crossover with another popular RPG like Dragon Quest. The characters from World of Final Fantasy could end up in the world of Dragon Quest, facing new enemies and having to adapt to different magic systems. For example, the mirages in World of Final Fantasy might interact in strange ways with the slimes in Dragon Quest.
A cool plot idea is an SI OC who is from a world where music has power. In Naruto, they discover that their musical abilities can either soothe or disrupt chakra. For example, they might be able to play a tune that calms down a rampaging bijuu. Another could be an OC that has the ability to see the past of a place just by touching the ground. This could lead to uncovering long - lost secrets about the founding of the ninja villages. Or perhaps an OC who can transform into different elements, not just the basic ones in the Naruto world, like turning into a magnetic field to disrupt enemy attacks.
One idea could be that the male self - insert (SI) has a unique power that complements Supergirl's. For example, he might have the ability to control technology, and together they fight against a cyber - villain who is trying to take over the city's power grid. Another plot could involve the male SI coming from a different dimension and having to adjust to the world of Supergirl while also helping her deal with an otherworldly threat that she's not familiar with. A third plot could be that the male SI is an ordinary human at first but gains powers through an accident and then he and Supergirl have to learn to work together as he masters his new abilities.
A great Naruto Final Fantasy fanfiction idea is to combine the magic systems. In this story, shinobi could learn to use Final Fantasy - style magic, like black magic for offensive spells and white magic for healing. Or perhaps a plot where the Akatsuki is after a powerful crystal from the Final Fantasy world that could grant them ultimate power. Also, a fanfic about a character from Naruto traveling through different worlds of Final Fantasy, facing the challenges and enemies in each world.