Another theme is the exploration of morality. 'ao no exorcist' has a clear divide between good and evil with the exorcists being the 'good guys' and demons the 'bad guys'. In 'kuroshitsuji', the line between good and evil is more blurred with Sebastian's complex motives. In crossovers, this moral ambiguity is often explored further as characters from both series interact.
One common theme is the clash of different power structures. In 'ao no exorcist', there are exorcist powers and demon - slaying swords, while in 'kuroshitsuji' there are demon contracts. When these two worlds cross, seeing how the characters with different power sources interact is a big theme.
I've also heard of 'Merged Realms'. It focuses on the cultural differences between the two universes. The more religious - based world of 'ao no exorcist' and the Victorian - era influenced 'kuroshitsuji' world clash and blend in interesting ways. The fanfic delves into how the characters adapt to these differences while also dealing with the overarching plot.
One common theme is the growth of their relationship. It often starts as a friendship and gradually develops into something more. Another theme is the acceptance of Rin's true nature. Shiemi is often there to support Rin as he comes to terms with his demon heritage.
A frequently seen theme is the interaction between different character personalities. In a crossover with 'Naruto', for instance, the determined and often hot - headed characters from 'Naruto' meet the more reserved or complex characters from 'Blue Exorcist'. This leads to some interesting character development and relationships. Also, the theme of good vs evil in a new context is common. Since both the original 'Blue Exorcist' and the crossed - over series usually have their own ideas about what is good and what is evil, it creates new scenarios to explore this concept.
One common theme could be friendship development. Since they are both characters in the Kuroshitsuji universe, their relationship might start as acquaintances and grow into a deeper bond in fanfics. Another theme might be adventure, where they go on some sort of journey together.
One common theme is the power dynamic. Ciel, as a human, has power over Sebastian in the sense of their contract, but Sebastian's demonic powers far exceed Ciel's. Another theme is loyalty and betrayal. There's always the underlying question of whether Sebastian will truly fulfill the contract or if he might find a way to betray Ciel. Also, the theme of revenge is prominent as Ciel is seeking revenge for his family's death and Sebastian is a key part of that journey.
One common theme is the forbidden love. Since Sebastian is a demon, a relationship with a human (the reader) is against the natural order. Another theme could be the power dynamic, as Sebastian has a lot of power and the reader may be in a more vulnerable position. And of course, there's the theme of mystery, as Sebastian's true motives and the nature of his relationship with the reader are often explored.
One interesting concept could be a crossover with other Victorian - era related works. It might bring in different characters and storylines from that time period, adding more depth to the Kuroshitsuji universe. For example, a crossover with Sherlock Holmes - like characters could lead to some exciting detective - related plots within the Kuroshitsuji world.
In 'Blue Exorcist Rin fanfic', a very frequent theme is Rin's battle against his inner demons, both literally and figuratively. His journey to master his demonic powers while still remaining true to his human side is often explored. Also, his relationship with the exorcist community, whether it's facing discrimination or finding acceptance among them, is a common theme. Additionally, his friendships, especially with the people he meets at True Cross Academy, are often a big part of the stories.
One common theme is the clash of different magical systems. Harry Potter has its own kind of magic with wands and spells, while Blue Exorcist has exorcism techniques. Another theme is friendship. Characters from both series often form new friendships or have to deal with differences in how they view friendship. For example, a Hogwarts student might be more used to having friends within their own house, while in Blue Exorcist, friendships are formed based on different criteria at the True Cross Academy.
One popular theme is the exploration of the complex relationship between Ciel and Sebastian. Many fanfics delve deeper into their master - servant bond, adding more emotional depth. Another theme is the alternate universes. For example, a modern - day setting where the characters have different roles but still retain their core personalities. Also, the backstories of the side characters are often explored, like the origin of Grell's unique personality and his relationship with other reapers.