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 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.
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.
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.
Typically, one common element could be the exploration of the character's emotions. Shinobu might experience a range of feelings like joy, fear, or anticipation. Another element could be how her relationships change, especially with those close to her.
A common theme is the power dynamic between them. Given Shinobu's powerful vampire nature and Araragi's somewhat normal yet complex character, their relationship often plays with who has more influence at different times.
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.
Love and family are common themes. It often shows how Sasuke and Hinata's relationship evolves with the new addition to their family. There's also the theme of anticipation and dealing with the changes that come with pregnancy.
Often, there are themes related to the challenges they face. For example, how they deal with the reactions of others in their world, be it friends or enemies. Also, the protection of the unborn child can be a significant theme, with Sesshomaru using his powers to safeguard Kagome and the baby.
One common theme could be the anticipation and preparation for the new life. This might include scenes of the character getting the nursery ready or shopping for baby items.