One common theme is the growth of their relationship. It often starts from a simple acquaintance and develops into a deep emotional bond. For example, they might start as comrades in the fight against demons and gradually fall in love.
Another theme is mentorship. Shinobu, being more experienced, often acts as a mentor to Tanjiro. She imparts her knowledge about demons and fighting techniques. This is seen in quite a few fanfictions where Tanjiro looks up to Shinobu for guidance.
One common theme is the exploration of their different personalities coming together. Tanjiro is very kind - hearted and Shinobu has a more complex, somewhat mysterious nature. Fanfics often show how they bridge that gap.
A frequent theme is secrecy. Shinobu's yandere feelings are often something she tries to hide from others, especially from Tanjiro at first. Also, the theme of protection can be seen. Shinobu may see her yandere actions as a way to protect Tanjiro from other threats, real or imagined. This can lead to some interesting plot twists as Tanjiro may not always understand her motives.
Often, there could be a theme of anticipation and hope. The story might focus on Shinobu's thoughts and feelings about the future with her unborn child. There could also be themes related to family, as she may think about the family she is creating or the family she came from. Additionally, themes of protection, both her protecting the unborn child and others protecting her during this vulnerable time, are also likely to appear.
One common theme could be the relationship between Tanjiro and other characters, often with a romantic or emotional undertone. Since it's a 'lemon' fanfic, there might also be some elements of physical attraction and intimacy, but presented in a way that is related to the story and the characters' development.
One common theme is the exploration of gender roles. Since Tanjiro is male in the original, making him female in fanfic allows for a look at how she would be treated in the demon - slaying world as a female. Another theme is new relationships. For example, how she might interact differently with other characters like Zenitsu or Inosuke as a female.
One common theme is the exploration of their contrasting personalities. Shinobu is often seen as more outgoing and mischievous while Giyuu is more stoic. Fanfics like to play with how these two different personalities interact and find common ground. Another theme is the idea of healing. Given their experiences in the main story, fanfics may show how they heal each other's emotional wounds.
Adventure can also be a big theme. They might go on quests or face challenges together, which strengthens their relationship. For example, in some fanfics, they have to defeat a common enemy while also dealing with their feelings for each other.
Love and friendship are very common themes. The fanfics often explore how the reader and Tanjiro develop a deep bond of love or friendship. Another common theme is adventure. Since Tanjiro is on a journey in the original story, many fanfics incorporate the reader into his adventures.
One common theme is friendship. They often start as comrades in the Demon Slayer Corps and develop a deep friendship. For example, they support each other in battles.