A common theme is the clash of different power systems. For example, when Shinobu crosses over into a world like 'Fullmetal Alchemist', her demon slaying powers contrast with the alchemy in that world.
One popular 'shinobu kocho crossover fanfiction' is the one where she crosses over with the world of 'Harry Potter'. In this fic, Shinobu's skills as a demon slayer are put to the test in the magical world. She might have to face new types of 'demons' in the form of dark wizards.
One common theme is the exploration of their relationship. Given their different personalities in the original work, fanfictions often focus on how they bridge the gap between them, like how Giyuu's stoicism and Shinobu's more cheerful yet calculating nature interact.
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 contrasting personalities. Shinobu is often seen as more light - hearted and talkative, while Giyuu is quiet and reserved. Fanfictions usually play with how these differences can either create friction or bring them closer together.
The themes usually include unspoken love. Since both characters are not very vocal about their feelings in the original story, fanfictions often explore the idea of them having deep, unspoken emotions for each other. Also, there's the theme of support. They support each other in battles against demons, and this aspect is often elaborated on in fanfictions, like how Shinobu's medical knowledge helps Giyuu when he's injured.
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.
One common theme is the exploration of their complex relationship. Given Shinobu's vampiric nature and Araragi's human - turned - vampire nature in a way, their relationship is full of power dynamics, loyalty, and a strange form of mutual dependence.
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 is the development of their relationship. It often starts from a place of mutual respect as fellow Demon Slayers and then progresses into something more like friendship or even romantic feelings. Another theme is how they support each other during battles. Since they both have their own strengths and weaknesses, they can complement each other well in combat scenarios in fanfiction.