Survival in a new world is also a frequent theme. When Naruto enters the Black Butler world or vice versa, they have to find a way to survive. They need to adapt to new rules, new enemies, and new allies. This theme often leads to a lot of action - packed scenes and character growth. The characters have to use their wits and abilities to make it through in this strange new place, and this can create some really exciting storylines in the crossover fanfictions.
Power dynamics is another theme. Naruto is a very powerful shinobi and in the Black Butler world, there are different power hierarchies. Fanfictions often play with how Naruto's power fits in or disrupts the existing power structures in the Black Butler universe. For example, how he might deal with demons or the Queen's orders. And also, friendship is a theme. Characters from both series form unexpected friendships, like Naruto befriending Sebastian. Their different personalities and goals make these friendships interesting to read about.
Power dynamics is also a common theme. Kaneki has his own set of powers as a ghoul, and the characters in Black Butler have their own abilities. Fanfictions might play around with who is more powerful in different situations or how they can use their powers together. Another theme could be the exploration of morality. Both series touch on moral grey areas, and in the crossovers, it can be interesting to see how the characters' moral compasses interact when they meet.
Character growth is also a common theme. Characters from both series are put in new situations. Naruto might have to adapt to the strict social hierarchies in the Black Butler world, and characters from Black Butler might learn from Naruto's values of friendship and determination. This allows for a lot of character development and makes the fanfictions more engaging as we see familiar characters evolving in new ways.
One common theme is the characters swapping worlds. For example, a character from Black Butler might end up in the wizarding world of Harry Potter, or vice versa. This creates interesting scenarios as they have to adapt to a completely different set of rules and cultures.
It could be really interesting. Sebastian from Black Butler might find Naruto's ninja world full of chaos and yet fascinating. He could use his butler skills to blend in, while Naruto might be intrigued by Sebastian's elegance and power. Maybe Sebastian would be tasked with protecting Naruto for some strange reason, like a contract made by the Hidden Leaf Village elders.
First, you need to do your research on both universes. Know the characters, their powers, and the settings well. For example, know all about Naruto's jutsus and Sebastian's demonic abilities. Then, think of a good plot device to bring the two worlds together. It could be a portal or a powerful spell. After that, start with an interesting introduction that hooks the reader, like Naruto suddenly finding himself in the Black Butler's Victorian - era London.
The theme of redemption is also quite common. Since Grell has done some rather dark things in the 'Black Butler' series, many fanfictions explore whether he can find redemption. Some stories show him trying to make amends for his past actions, either through helping others or by changing his ways. And of course, the theme of friendship or camaraderie among the reapers, especially with Grell, is often explored. We see how he interacts with other reapers and how those relationships develop or deteriorate in different fanfictions.
One common theme is obedience. Since discipline often implies following rules or orders, many fanfictions explore how the characters in Black Butler, like the servants in the Phantomhive manor, learn to be obedient. For example, they might face consequences if they don't follow Sebastian's instructions.
One common theme is the idea of rebirth or transformation into a baby form. This often leads to a change in the power dynamics between characters. For instance, a powerful character like Ciel becoming a baby makes him vulnerable, and other characters have to step up to protect him.
Another theme is sacrifice. In many fanfictions, the characters are willing to sacrifice a great deal for their love. This could be their status, their safety, or even their own lives. It adds a sense of drama and intensity to the romantic story. For instance, a character might risk everything to be with the one they love in a world full of danger and mystery.
Another theme is his past as a soldier. Fanfictions like to expand on his military experiences, like how he dealt with the trauma of war. It could be about him having nightmares and how he overcomes them while serving the Phantomhives.