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.
I'm not sure if there is a specific fanfiction exactly like that. Fanfiction can cover a wide range of scenarios and pairings, but this particular one might be a bit unusual considering the nature of the characters in the original story. You could try searching on major fanfiction websites to see if such a story exists.
There are many fanfictions out there with all kinds of creative and often out - of - the - ordinary concepts. However, this particular idea seems rather unusual and not in line with the traditional characteristics of the Inuyasha series. In the original series, both Koga and Inuyasha are male characters, and pregnancy in a male - male relationship is not a part of the original story's biological framework. But in the world of fanfiction, writers can bend the rules and create unique scenarios, so it's possible that such a fanfiction exists, but it may not be a common or mainstream one.
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.
Yes, there might be such fanfiction in some fan communities. However, this often goes beyond the original storyline of the 'Inuyasha' series. Fanfiction can explore various 'what - if' scenarios, but it's important to note that not all fans may be comfortable with this particular plot direction.
One idea could be that their relationship starts as an unexpected alliance against a common enemy. As they spend more time together, they gradually develop feelings. When Kagome discovers she's pregnant, it could bring a new level of complexity to their relationship. Sesshomaru, being a proud demon, might initially struggle with the idea of impending fatherhood but then grow into a protective and loving partner.
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.