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.
One consequence could be a shift in the power dynamics. Since Sesshomaru is a very powerful demon, his being Inuyasha's father might mean that Inuyasha has access to more power or knowledge. For example, Sesshomaru could train Inuyasha in ways that no one else could.
Well, it's a really strange crossover concept. Inuyasha is from a very different universe than Harry Potter. But if he were to be Harry's father in fanfiction, it could involve some time - travel or interdimensional magic. Maybe some dark wizard used a spell to bring Inuyasha to the wizarding world and he had a relationship with a witch. However, it would be a huge stretch of both universes' lore.
The storyline could be quite interesting. Inuyasha might introduce a whole new way of fighting dark magic with his combat skills. He could train Harry in a more physical and aggressive style compared to the normal wizard dueling. Also, the relationship between Harry and his friends might change as they try to understand his half - demon heritage.
In the fanfiction, when Inuyasha meets his father, there could be a display of power. His father might teach him some new combat skills or give him advice on how to better control his demon side. It could also be an emotional moment, with Inuyasha finally getting the fatherly guidance he never had growing up.
Fanfiction often takes liberties with the relationship between Izuku and Toga. It could also involve them teaming up against a common enemy. This would require them to put aside their differences and work together. Writers can use this to create exciting action - packed scenes and explore how they would communicate and cooperate in such a situation.
Toga is still alive in the manga. The creators haven't decided to end her character's journey with death. Usually, such major plot points are well-signaled and haven't happened for Toga so far.
He might be shocked at first. After all, he has probably only heard stories about his father. Then he could be angry, blaming his father for not being around when he was growing up.