It could be possible in a fanfiction where the rules of the original universes are bent. For example, if there was a powerful magic or some sort of super - science at play. The universes of Naruto and Harley Quinn are both filled with extraordinary elements. So, if a writer wants to create a scenario where Naruto is Harley Quinn's son, they could introduce a concept like a reality - warping device that merged parts of their worlds and created this strange family connection.
In fanfiction, the idea of Naruto being Harley Quinn's son might start from a creative exploration of contrast. Naruto is all about honor, hard work, and friendship in his ninja world. Harley Quinn is this unpredictable, chaotic character in Gotham. Combining them in a family relationship can create a really interesting dynamic. A writer might imagine that some sort of interdimensional travel went wrong, and Naruto ended up in Harley Quinn's world as a baby. Harley, with her own brand of crazy - loving nature, decided to raise him, thus making him her son in this fan - created scenario.
Well, in fanfiction, anything can be possible. Maybe some sort of multiverse theory could be applied. A strange rift in the fabric of the universes could have occurred, pulling Naruto from his ninja world into Harley Quinn's chaotic Gotham - like world. And then, through some really wild and unthinkable circumstances, they end up in a situation where Naruto could be seen as her son. Maybe Harley Quinn took in Naruto when he was lost in her world and raised him as her own.
In fanfiction, the idea of Naruto being Mirajane's brother might be achieved through some creative plot devices. For example, it could be a result of some time - traveling or dimension - hopping event. A wizard or a ninja with special abilities accidentally merges their two worlds in a way that Naruto and Mirajane end up being related as siblings. This allows the writer to explore how characters from two very different series would interact within a family dynamic.
In a fanfiction scenario, it might be possible if there was a powerful Sith artifact that somehow ended up in the Naruto world. Naruto, being curious and perhaps a bit naive at first, gets too close to it. The artifact starts to corrupt him, slowly turning his ideals and powers towards the dark side, similar to how Darth Sidious rose to power. This would be a long and complex transformation, changing Naruto's personality and abilities to be more like the Sith Lord.
One way to make a 'Naruto and Bellatrix' fanfiction work with their different universes is to focus on the characters' personalities. Naruto is known for his determination and his belief in the good in people. Bellatrix is a complex character, loyal to Voldemort but also having her own desires. In a fanfiction, Naruto could try to show Bellatrix a different way of life. He could introduce her to the concept of friendship and loyalty in the ninja way. And Bellatrix could show Naruto the power and mystery of magic. Their interactions could lead to changes in both of them, and the different universes could serve as a backdrop to their character development.
Perhaps Naruto is raised in a world where both the Naruto and DC elements are combined. He grows up learning ninjutsu but also has a penchant for Harley Quinn - like pranks. His story could be about him trying to bring peace to this mixed - up world. He uses his Rasengan in new and creative ways, like adding some of Harley's acrobatic flips to his attacks. And he has to deal with villains who are also a combination of Naruto - style bad guys and DC villains.
In alternate universes where Gotham has different power dynamics, their love can change. If Harley has more power, she might be the one to pursue Batman more aggressively. Or if Batman is part of a team - up against a greater evil, their love could be a side - plot that shows how they work together and grow closer through shared experiences. Their love is often shaped by the unique rules and characteristics of each universe.
Fanfiction is all about bending the rules. Regarding Hermione being Clint's daughter, it could start with a plot device like a time - travel or dimension - hopping accident. Imagine Hermione gets lost in a different dimension where Clint is. He takes her in and raises her as his own. Her magical abilities could be a secret that she has to hide in this new world, which would add a lot of interesting plot twists and character development to the fanfiction.
Fanfiction is all about creativity and bending the rules. Regarding Hermione being John Winchester's daughter, it could be that the writer wants to explore the contrast between Hermione's magical world and John Winchester's world of hunting supernatural beings. Maybe Hermione discovers her true heritage through a series of adventures that bridge the two worlds. It could also be a way to combine the themes of magic and the fight against evil in a new and interesting way.
It could be someone who wants to use Naruto's unique heritage against him. Maybe a villain from the Naruto universe who sees Naruto's connection to Harley Quinn as a weakness. For example, Orochimaru might want to capture Naruto to study his strange combination of powers.
The story could start with a strange portal opening in Gotham City. Out comes Naruto, all confused about this new and dark place. Harley Quinn, who was just about to cause some trouble, sees Naruto and is intrigued. She approaches him, not knowing what to make of this strange - looking boy with orange clothes and a headband.
In this fanfiction idea, it might be that a powerful being from a higher dimension decides to mess with the fates of these two universes. They could manipulate the timelines and genetics in such a way that Naruto is born as Toriko's son. This would completely change Naruto's backstory and his relationship with the Hidden Leaf Village. He might grow up with a whole new set of values and powers influenced by Toriko's world, like having a stronger focus on food - based powers or a different view on combat.