She could be integrated through her design skills. Imagine she creates a new, more efficient Bat - suit. This not only improves Batman's capabilities but also gives her a role in the Bat - family. Also, her positive attitude can contrast with Batman's often - gloomy outlook, adding an interesting dynamic to the story. She might also introduce some elements of magic from her world, which is quite different from the more gritty and realistic Batman universe, but in a way that enriches the story.
One way to integrate them is by exploring similar themes. All three have elements of heroism and facing great challenges. The Shinju represents a powerful and often dangerous force in Naruto. In Batman's world, there are powerful villains. A fanfiction could bring these together by having Batman face a threat related to the Shinju, with help from Naruto characters. They could also explore the different concepts of justice in both universes.
Marinette might develop more empathy. Going through pregnancy gives her a new perspective on life. She may understand the struggles of others better, like those who are vulnerable or in need of protection, which could influence how she acts as Ladybug.
Marinette might start off as a scared and confused character when she first enters the League of Assassins. But as time passes, she would become more determined to survive. She would gradually learn the ways of the assassins and use her own unique skills to her advantage. Her development could also involve her becoming more assertive and confident in her abilities.
Marinette's character can be developed through her angry outbursts. For instance, when she gets angry, we might see her make rash decisions that she later regrets. This shows her impulsiveness when overcome by anger. Also, her anger could lead to her learning new ways to control her emotions, which is a part of her growth. Maybe she starts to practice meditation or some other calming techniques, which changes her character over time.
She may become more resilient. The torture is likely to test her limits, and through it, she'll grow stronger in spirit.
They can be integrated through crossovers. For example, Harry could end up in Gotham due to a magical accident and team up with Batman. Their different skills would complement each other. Harry with his magic and Batman with his combat and detective skills.
Aphrodite can be integrated by having her interfere with the love potions in the Harry Potter world. Since she is the goddess of love, she might have her own take on how love potions should work or might even try to create a more 'authentic' form of love magic. For instance, she could find the existing love potions too artificial and introduce a new kind of potion that is based on true love rather than just infatuation.
Sabine could be integrated as a foreign exchange student from a magical school in another part of the world. She could bring her own unique set of magical abilities and cultural beliefs related to magic. For example, if she has a different way of casting spells or making potions.
One way is to make the human a wandering knight. This knight, while passing through Sherwood Forest, hears of Robin Hood's noble deeds and decides to join forces with him. The knight could bring in his own code of chivalry and fighting skills. His presence could also attract more attention from the outside world, both good and bad, to the forest community. This would add more excitement and new plotlines to the fanfiction.
Orihime could be a part of a cross - dimensional experiment gone wrong. So she ends up in the Naruto world. Her presence could disrupt the existing balance, and the story could revolve around how the characters deal with this new, powerful, and somewhat naive character. She might start off as a bit of an outcast because of her different abilities and way of thinking but gradually find her place among the ninja.