Well, it might start with the female Inuyasha being chased by some demons and accidentally finding herself in the lair of Sesshomaru's mother. The mother might be intrigued by this strange version of Inuyasha. She could test the female Inuyasha's worthiness in some way, like through a series of trials. If the female Inuyasha passes, she could gain the mother's respect and perhaps even an alliance. This could then lead to a whole new set of adventures where they work together to maintain the balance in the demon world.
One possible plot could be that the female Inuyasha stumbles upon Sesshomaru's mother's territory while on a journey. Maybe she's in search of something, like a powerful artifact. Sesshomaru's mother, being a powerful and mysterious figure, initially sees her as an intruder. But as the female Inuyasha shows her tenacity and perhaps a bit of kindness, they start to have a more amicable relationship. The female Inuyasha could learn some ancient secrets or powers from her, which she then uses to help her friends or to face her own inner demons.
The plot could involve the female Inuyasha having a premonition that Sesshomaru's mother holds the key to her past. So she sets out to find her. When they meet, Sesshomaru's mother is initially cold and distant. However, as the female Inuyasha shares her story, the mother realizes there are deeper connections between them. They could then embark on a journey together, with the mother teaching the female Inuyasha about the history of their kind and how to better control her powers. This newfound knowledge could change the female Inuyasha's life and her place in the world of demons and humans.
One possible plot twist could be that Sesshomaru initially mistakes Kagome for someone else. Maybe he thinks she's a powerful priestess from his past. This could lead to an interesting dynamic where he's initially hostile but then realizes she's not who he thought. And it might change his view on humans in general as he gets to know Kagome better.
One possible plot twist could be that Sesshomaru's mother initially mistakes Kagome for a threat and tries to attack her. But then, upon realizing Kagome's connection to Inuyasha and her kind heart, she decides to protect Kagome instead. This would completely change the dynamic between them from hostility to an unlikely alliance.
It could be described as tense at first. The female Inuyasha would be on guard, her ears perked up, and her sword at the ready. Sesshomaru's mother, with her regal and intimidating presence, would look down on the female Inuyasha. But as they exchange words, there could be a sense of mutual curiosity. The air would be filled with a strange energy, a mix of suspicion and the potential for something more, like an unexpected friendship or alliance.
One possible plot could be that Kagome stumbles upon Sesshomaru in the forest while she is separated from Inuyasha and the others. Sesshomaru, being his proud self, initially views her as a nuisance. But as she shows no fear of him and even tries to communicate in her kind - hearted way, he starts to be intrigued by this strange girl with spiritual powers.
There might be a plot where Sesshomaru's pride initially makes him reject the idea of being involved in such a situation. However, as the story progresses, his sense of honor towards Inuyasha, who is now carrying his child, starts to develop. The fanfic could also show Inuyasha's struggle with his new physical state and how he has to adapt to it while still being the feisty character he is.
One common theme is the exploration of a different dynamic between them. Since Inuyasha and Sesshomaru have a complex relationship in the original series, in fanfics with female versions, it could be about them forming an unexpected alliance. Another theme is romance. Fans often like to write about a romantic relationship developing between the female Inuyasha and Sesshomaru, which could be a slow - burn or a more sudden attraction.
It would likely cause a shift in the power dynamics. Inutachi has been managing on their own for a while, but Sesshomaru's mother's presence would change that. She might be much more powerful and her decisions could influence the direction in which Inutachi's journey is headed. Say, she could decide to send them on a new quest or protect them from a new threat.
One common theme is family. Since they are brothers, these fanfics often explore their family ties, like how their father's absence or presence affected them as babies. Another theme is rivalry. Even as babies, their different natures could lead to a sort of rivalry, which is often explored in these fanfics.
One plot idea could be that Sesshomaru has to raise Inuyasha in a world where all the other demons are against them being together. He has to teach Inuyasha how to control his powers while also protecting him from various threats.
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.