Perhaps a story about a love that bridges two rival clans. A member of one clan and a member of another fall in love and try to find a way to bring peace between their clans instead of war. This could involve them facing many challenges from within their own clans who are against their relationship.
Another plot could be a clan that is wrongly accused of a heinous crime during the war. They have to fight not only the other six clans but also clear their name. A young detective - like character within the clan could start investigating the real culprit to prove their clan's innocence.
A plot could revolve around a time - travel fanfiction. Maybe a character goes back in time and has to prevent an event that would have a catastrophic effect on the future of the Trinity Seven world. This could involve interacting with younger versions of the characters and changing their fates.
A great plot for Magnificent Seven fanfiction might be a love story within the group. Perhaps one of the members falls in love with a local girl they are protecting. But there are complications, like her father doesn't approve because he thinks the man is too dangerous. And at the same time, they still have to face off against the bandits that are threatening the town. So it's a story of love and duty all mixed together.
Another idea is that Naruto goes back in time and teams up with a young and idealistic member from each warring clan. Together, they form a sort of secret alliance with the goal of promoting peace. They face many challenges, like convincing the more conservative and power - hungry members of their clans that peace is a better option. Along the way, Naruto also has to deal with the fact that his presence in the past might be changing the future in unexpected ways.
One idea could be creating an OC who is a long - lost relative of one of the main characters in the Magnificent Seven. This OC could bring a new dynamic, perhaps with a secret past or a special skill that helps the group in a unique way. For example, if the OC is related to Vin Tanner, they might have a similar tracking ability but with a different approach.
One idea could be to introduce a new character who has a special skill, like being an expert archer from a far - off land. This character could initially be distrusted by the group but then prove their worth in a big battle. Another idea is to have a plot centered around a lost treasure that the group has to find while also dealing with a rival gang who wants it for themselves. Maybe the OC could have a personal connection to the treasure's origin.
Perhaps a crossover where the Trinity Seven characters enter a post - apocalyptic world. Their magic would be both a great asset and a source of danger as other survivors might see them as threats or saviors. They'd have to figure out how to survive and maybe even find a way to restore the world using their powers.
One idea could be exploring the backstories of each member of the Band of Seven in more detail. For example, how they came together and what their individual motives were before joining the group.
Perhaps a great plot idea would be to have a character who is an outsider to the Keyblade War but gets dragged into it. This character could bring a fresh perspective and different skills or abilities. They might try to find a way to end the war through negotiation rather than fighting, which would add a whole new layer to the story. And you could also explore how the power of friendship and trust can be a game - changer in the midst of all the chaos and battles.
Maybe there's a character who has the ability to traverse different universes freely in this 'the multiverse at war fanfiction'. Their journey to find a way to end the war by uniting the different versions of heroes from various universes would be really engaging. They might face challenges like different versions of the same villain trying to stop them.
A time - travel plot would also be great. Imagine a character from the future coming back to the time when Kaguya and Miyuki were just starting their 'war'. This new character could either try to help them get together faster or, for some reason, try to keep them apart. It would add a new layer of mystery and drama to the fanfiction.