Another unique way is to have an Incubus be the key to unlocking a hidden power within Naruto. Maybe the Incubus has a special connection to an ancient and forgotten power source in the Naruto world. When Naruto encounters the Incubus, it sets off a chain of events that leads to him accessing this new power, which is different from his normal Sage Mode or other known powers.
You could make it so that a character from the Fullmetal Alchemist universe ends up in the Naruto world and teaches Naruto and his friends fire alchemy. This would lead to some interesting cultural clashes and exchanges. They could combine the principles of alchemy with chakra control in ways that are completely unexpected, like creating new types of ninja tools using alchemical transmutation.
Well, often in such fanfiction, the incubus is made to fit the power systems of Naruto and Rosario Vampire. In Naruto, if we think about it, the incubus might have some jutsu related to seduction or mind control which could be a really interesting addition. In Rosario Vampire, it could be part of the hierarchy of monsters. Maybe it has a special connection to the vampires, like being able to influence their bloodlust in some way. So, it really depends on how the author wants to blend these different elements together.
One way is to have a Creepypasta - like curse befall Hogwarts. For instance, a curse that makes the staircases move in a truly chaotic and disorienting manner, similar to the unease that Creepypasta stories create. The students would have to navigate this new and scary situation, perhaps with some help from the teachers who are also baffled by this strange occurrence.
Well, fireworks can be used as a symbol. For example, in a fanfiction, every time Batman has a major victory, the people of Gotham set off fireworks. It becomes a sign of hope. Or, a new villain could create fireworks that are actually small bombs disguised as regular ones. Batman has to quickly learn to tell the difference to stop the villain's attacks.
A unique way could be to have the Kyuubi's chakra be tied to the bikini. For example, the more powerful the Kyuubi's chakra, the more elaborate and magical the bikini becomes. Naruto has to learn to control this new aspect of the Kyuubi's power as they go on a journey to save the village from a new threat. This would add a fresh twist to the typical Naruto and Kyuubi relationship.
In a unique fanfiction, the Eight Celestial Gates could be tied to emotions. For example, the first gate is linked to anger, the second to sadness, and so on. Naruto has to face and control these emotions to open the gates. This would add a psychological and emotional depth to the story as he battles not just external enemies but also his internal feelings.
The lemon element can be used in a unique way by making it a key to unlocking hidden realms. Naruto and his summons find out that there are special lemon - shaped keys that can open portals to different dimensions. These dimensions are filled with challenges and treasures. As they search for these lemon keys, they face various enemies and obstacles, and the story can revolve around their adventures in these new realms that are only accessible through the power of lemons.
Foxes could be part of a new magical species in the fanfiction. They could have their own language and culture within the wizarding world. For instance, they might live in a hidden part of the Forbidden Forest and have a special connection to nature magic that the main characters need to understand to defeat a new dark force. This would expand the world - building in the fanfiction.
The human could be reincarnated as a car in the fanfiction. This would give them a completely new life as a vehicle. They would have to learn the rules of the road in the Cars world, which might be different from what they knew as a human. For example, traffic laws could be based on different things like horsepower limits in certain areas or special racing lanes for high - performance cars. This reincarnation could also lead to them having a different personality as a car compared to when they were human.
One unique way is to make Ultra Instinct a power that is passed down through generations in a hidden family line within the RWBY world. For instance, Blake could discover she has this heritage and starts to unlock Ultra Instinct. Another way is to have it be a power that is only accessible in a certain location, like a forgotten temple in the Ever After. Characters would have to journey there and face trials to gain Ultra Instinct.