Perhaps there is a prophecy in both worlds that foretells the coming together of a dragon - slayer and a kunoichi. Natsu and Sakura, not knowing about this at first, are drawn to a special place that exists between their two worlds. Here, they find that the laws of magic and chakra are intertwined. They start to experiment with combining their powers. Natsu's fire magic could be combined with Sakura's fire - based ninjutsu to create a new and powerful attack. This discovery makes them realize the potential of their two worlds working together and they set out to make it a reality.
One way would be through a magical portal. Maybe some dark magic in the 'Fairy Tail' world accidentally creates a portal that sucks Sakura into it. Once in the Fairy Tail world, she has to adapt quickly. Natsu could be the first to find her. He's initially confused by her ninja abilities but soon realizes they can be useful. They then work together to close the portal that's causing chaos in both worlds. In this way, the two worlds start to blend as they exchange knowledge and skills.
In the fanfic, it could be that a powerful enemy is threatening both the ninja world and the Fairy Tail world. This enemy has the ability to traverse between the two dimensions. Natsu and Sakura are chosen as representatives of their respective worlds. They meet and start to combine their unique powers. For example, Sakura could use her chakra - enhanced strength to help Natsu in a physical fight, while Natsu's magic could enhance Sakura's ninjutsu attacks. This cooperation would bring the two worlds closer together as they fight for the common good.
It could be a really interesting crossover. Natsu is from 'Fairy Tail' with his powerful fire magic and hot - tempered nature. Sakura from 'Naruto' is a strong - willed kunoichi. Maybe in the fanfic, they meet in a strange new world created by some magical or ninja - related event. They could start off as rivals, not understanding each other's powers at first. But as the story progresses, they learn from each other and combine their skills to face a common enemy.
It could be that there's a shared villain. A powerful entity that is causing problems in both the Pokemon world and the Danny Phantom world. The girl and Danny join forces to take on this villain. They combine their unique abilities, like the girl's Pokemon training skills and Danny's ghost powers to fight the bad guy.
If we consider a Naruto and Jessica Rabbit fanfic, their worlds could blend in a number of ways. For instance, Naruto's world has chakra, which is a form of energy. Jessica Rabbit's world has a certain kind of magic or allure. They could find that these two forms of power have some similarities. Maybe they could combine their powers to defeat a common enemy. Naruto could use his shadow clone jutsu, and Jessica could use her charm to distract the enemy while the clones attack.
Well, some fanfics blend the two worlds by making 5sos be related to some wizarding families. So, they already have a connection to the wizarding world without really knowing it. Then, as they discover their heritage, they get involved in the Harry Potter storylines. It could be that one of the 5sos members has a long - lost wizard relative and that's how they are drawn into the magical universe. This way, the two worlds are intertwined in a more family - based way.
It could blend the two worlds by having a common enemy. Let's say a powerful being that threatens both the ninja world and the world of Greek mythology. Percy and the Naruto characters would have to team up. The Mokuton abilities could be used in unique ways to fight this enemy. For instance, creating huge wooden barricades to hold off the enemy's attacks while Percy uses his powers to strike from a distance. The two worlds' cultures and powers would mix as they strategize together.
In a Naruto - Vikings crossover fanfiction, the power systems could be really interesting to combine. The Vikings have their physical strength and combat skills, while the ninja in Naruto have chakra and jutsu. Maybe a Viking could be exposed to chakra and start to develop their own unique form of jutsu based on their Viking heritage. For instance, a Viking with a connection to Thor could use lightning - based jutsu in a way that's different from how a normal Naruto character would. This would create a whole new dynamic in the story as the Vikings and Naruto characters learn from each other's powers.
A possible way to blend the two in a fanfiction would be through the power systems. In Naruto, there's chakra, and in Soul Eater, there are souls and soul wavelengths. The fanfiction could create a connection where chakra is related to the strength or quality of a character's soul. So Naruto characters with high - level chakra like Naruto and Sasuke would have very powerful souls in the Soul Eater world. Also, the different jutsu in Naruto could be adapted to deal with soul - related problems in the Soul Eater world, like using Fire Style jutsu to burn away corrupted souls.
The characters would have interesting interactions. Naruto, being the energetic and friendly hero, would likely make friends quickly in the Demon Slayer world. He'd probably be fascinated by the swords and the concept of demon slaying. And the Demon Slayer characters would be intrigued by Naruto's shadow clones and other jutsus. They could learn from each other and develop new strategies for fighting enemies. For example, Naruto could show them how to use mass - produced clones for distraction while the Demon Slayers attack from a different angle.
In this fanfiction, the blending might occur when a group of wizards decides to study Muggle technology to gain an edge in the fight against Voldemort. They stumble upon the concept of the atomic bomb. Harry Potter then gets involved as he tries to prevent the wizards from misusing this knowledge. The story could show how the different cultures and power systems of the wizarding and Muggle worlds collide and interact around the idea of the atomic bomb.
In a Pokemon Beauty and the Beast fanfic, the setting could be in a unique region where a certain Pokemon has been cursed. For example, a Luxray that was once noble and beloved has been turned into a more savage form. A young Pokemon researcher, the 'Beauty' in this story, decides to study the Luxray and in the process discovers the truth behind the curse. By using her knowledge of Pokemon behavior and a special item she found, she manages to break the curse and restore the Luxray to its former self. This fanfic could explore themes of redemption and the power of understanding.