You could also do a story where a character from the Fantastic Beasts world, like Tina Goldstein, travels to the Naruto world. She could learn about chakra and ninjutsu while also teaching the Naruto characters about the different types of magic in her world. This would lead to some interesting cultural exchanges and new friendships.
One idea could be to create a crossover where Naruto characters visit the world of Fantastic Beasts. For example, Naruto could befriend Newt and they go on an adventure to find a lost bijuu that has somehow ended up in the Fantastic Beasts universe. It would be exciting to see how Naruto's ninja skills would interact with the magic in that world.
Perhaps a dark wizard in the Fantastic Beasts world tries to use Merlin's power for evil. Merlin has to team up with Newt and Tina to stop this wizard. Along the way, Merlin discovers new magical abilities within himself as he faces the different magical challenges presented by the Fantastic Beasts world.
One idea could be an OC who is a secret healer for magical creatures in the Fantastic Beasts universe. They could have a special connection with a rare and endangered beast, like a Thunderbird. The OC's mission could be to protect the beast from dark wizards who want to use its power for evil.
One idea could be exploring the backstory of a minor character from the series in the fanfiction. For example, delving into the early life of Luna Lovegood's father. Another could be a story where a new magical creature is discovered in the Forbidden Forest and how the Hogwarts students interact with it. Or perhaps a fanfiction where the events of the Fantastic Beasts movies intersect more directly with the main Harry Potter storyline, like Newt Scamander visiting Hogwarts during Harry's time there.
One idea could be that Newt Scamander visits Hogwarts to give a special lecture on fantastic beasts. During his visit, he discovers a hidden magical creature that has been living in the Forbidden Forest for centuries. Harry Potter and his friends get involved in helping Newt study and protect this new discovery.
Some fanfictions might explore what would happen if a Fantastic Beast escaped into a non - magical world. Picture a story where a Thunderbird ends up in a big city like New York in the Muggle world. How would the Muggles react? And how would Newt and his friends try to retrieve it without causing too much chaos and without revealing the wizarding world?
A great plot could involve the male OC traveling to a different wizarding country in search of a cure for a magical disease that is affecting his loved ones. Along the way, he meets all sorts of interesting characters and has to face different magical challenges. Or he could be part of a secret society within the wizarding world that is trying to preserve a certain type of magic that is being threatened by modern technology. He has to fight against those who want to get rid of this old magic.
A great storyline could also be a crossover within the Harry Potter universe. Imagine a situation where characters from the Harry Potter books meet those from the Fantastic Beasts world. Maybe Harry and his friends stumble upon Newt's case of beasts during one of their Hogwarts adventures, and they have to work together to solve a problem caused by a mischievous beast that has escaped.
One idea could be that the female tailed beasts team up with Naruto to protect the Hidden Leaf from a new and powerful enemy. They use their unique powers in combination with Naruto's skills to create some really cool battle scenes.
One interesting plot idea could be Naruto having to form a special bond with each tailed beast separately. For example, he might start with the One - Tailed Shukaku and have to understand its past and the pain it has endured. This could involve him entering the tailed beast's mind - scape and facing its inner demons. Another idea is that all the tailed beasts decide to test Naruto's worthiness as the Jinchuriki of the Nine - Tails. They could create various challenges for him, both physical and mental, to see if he can truly handle the power of all the tailed beasts combined. A third plot could be that an ancient evil threatens the world, and only by uniting all the tailed beasts and their powers, with Naruto as the leader, can they defeat it.
One plot idea could be that the female tailed beasts are initially distrustful of Naruto. But as they interact more, they discover his pure heart. For example, the Two - Tails might be constantly on edge around Naruto at first. Then Naruto saves her from a powerful enemy, and she starts to respect him. Another idea is a love triangle between Naruto and two of the fem tailed beasts, like the Five - Tails and the Eight - Tails. This could create a lot of drama and tension in the story.