A really interesting plot twist could be related to her heritage. Since Rin is the son of Satan in the original, as a girl, there could be some unique take on that. Maybe there are different expectations from the demon world for a female heir of Satan. This could lead to different power manifestations or different temptations that she has to face compared to male Rin.
One common plot twist could be that Rin, as a girl, has a different approach to her exorcist training. Maybe she uses her femininity to her advantage in a way a male Rin couldn't. For example, she might be more perceptive to the emotional states of the demons she encounters, which could lead to either more successful exorcisms or getting into more dangerous situations because she gets too involved.
Some fanfics focus on Rin's power development in a different way from the original story. Maybe she discovers new powers or has to learn to control her existing ones in a more challenging situation. There are also fanfics that explore Rin's family relationships in more depth, especially her connection to her father. This could involve flashbacks or new revelations about her family's past.
One common theme is innocence. Since it's about 'baby Rin', it often shows his pure and naive side before he fully understands the weight of his demon heritage. Another theme is friendship. It might explore how Rin forms his first friendships at the academy.
One possibility could be that his relationships with other characters would change drastically. For example, his friendship with Yukio might become more protective on Yukio's part as he now has a sister - like figure in Rin. Also, his interactions with the other exorcist trainees could be different. They might be more hesitant around him as a girl, or some might be overly friendly in a different way.
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 power struggle. Given that Rin is a powerful exorcist and Amaimon is a demon, there's often a tug - of - war between their powers and how they deal with it in their relationship. Another theme could be the exploration of their different natures, with Rin being half - human and half - demon and Amaimon being a full - fledged demon.
A unique plot idea could be that Rin's tail has a mind of its own and can communicate with other demonic entities. This would lead to some really interesting situations where Rin has to deal with the advice or demands of his tail.
In a fanfic where Rin is secretly a girl, the author could explore themes of identity and self - discovery. Rin might struggle with coming to terms with her true gender while also dealing with the challenges of being an exorcist. It could add a whole new layer of depth to the character and make for a very engaging story.
One common theme is the growth of their relationship. Since Rin is a demon - human hybrid and Shiemi has her own insecurities, their relationship development is often explored. For example, how they learn to trust each other more deeply.
Love and friendship are also big themes. The relationship between Rin and the OC can range from a slow - burning friendship that turns into love, to an instant attraction. In many stories, they support each other through difficult times, like when facing powerful demons or dealing with the politics within the exorcist community.
One great aspect of Blue Exorcist Rin and Yukio fanfiction is the exploration of their brotherly bond. Writers often delve into how they support each other through their difficult exorcist training and the challenges of their unique heritage. For example, in some fanfictions, they might have to face a particularly powerful demon together, and through this, their relationship deepens as they rely on each other's strengths.