It would completely disrupt the existing power balance. Their relationship would shift from one of rivalry to something extremely complex. It could also change how other characters interact with them, as this new situation would be so out of the ordinary.
One idea could be a story where a powerful magic affects both Sesshomaru and Inuyasha, causing them to be in a situation where they have to deal with the unexpected pregnancies. This could lead to them having to put aside their differences and work together to understand what's happening to them. Maybe they go on a journey to find a cure or a way to handle the situation, all while facing various challenges from other demons who see their condition as a sign of weakness.
Sesshomaru would be very much in control of his emotions on the surface. But deep down, he'd be worried about how this would affect his status among the demons. He might start to question his own identity and what it means to be a demon in this new situation. His reaction would be slow - evolving as he tries to understand the implications. Inuyasha would initially be in disbelief, but as he starts to feel the baby move or experience other symptoms, he'd have a complete change of heart. He'd become more responsible and start thinking about how to provide a better future for the child. He might also have to deal with his own insecurities about being a good father, given his own troubled past.
Well, in the vast world of fanfiction, there are all kinds of wild and creative ideas. But in the context of the Inuyasha canon, this is really out of the ordinary. Sesshomaru and Inuyasha have a long - standing enmity and different personalities. Their relationship is mainly centered around power struggles and family issues rather than this kind of very unorthodox situation.
In some fanfictions, Sesshomaru being Inuyasha's father can lead to really interesting plot developments. For example, it can create complex family dynamics. There might be stories where Sesshomaru has to come to terms with his new - found fatherhood and how it changes his relationship with Inuyasha, who he may have previously seen as an enemy or a rival. It also allows for exploring Inuyasha's feelings towards having a father figure like Sesshomaru, who is such a powerful and complex character in the Inuyasha universe.
In fanfiction, many things are possible outside the normal canon of the Inuyasha universe. It could be that a creative writer has imagined a scenario where Kagome and Sesshomaru have a relationship that leads to pregnancy. Maybe there's some magic or a unique plot device that brings them together in this unexpected way.
One common theme could be the exploration of their relationship transformation. From being enemies or at least not on friendly terms, they now have a very intimate connection through the pregnancy. Another theme might be the acceptance within their society. Since this is such an unusual situation, how do the other demons or humans around them accept or reject this union and the upcoming child.
Sesshomaru would raise the baby with a combination of discipline and protection. He would protect the baby from any threats, using his powerful abilities. At the same time, he would discipline the baby when it made mistakes, teaching it the ways of the demon world. Inuyasha, on the other hand, would add a more carefree and emotional touch to the parenting, creating a balance in the baby's upbringing.
In fanfiction, the baby could be the key to unlocking some long - lost secrets in the Inuyasha universe. Since Sesshomaru and Inuyasha have such complex histories and lineages, the baby might hold the answers to ancient prophecies. It could also have a special bond with the Jewel of Four Souls, perhaps having a unique way of controlling or protecting it that neither of its parents had. And of course, there would be all kinds of emotional drama as the two brothers - turned - co - parents deal with their new relationship.
The theme of coexistence is also quite prevalent. Given their different natures and goals, fanfictions explore how they can live in the same world. Some stories show them finding a balance between their demon and human sides, which is related to their individual identities. It's about how they can tolerate and even support each other in a world that doesn't always accept them for who they are.