The baby in the fanfiction could be of a special lineage. It could have powers that Sesshomaru needs to understand and help develop. This would lead to a journey of discovery for him. He may also have to face his own past traumas related to family as he raises the baby, and this could be a way to heal his inner wounds.
One way could be to show Percy's internal struggle. He might initially try to hide his illness from his family because of his pride and the distance he had with them before. For example, he could keep going to work at the Ministry, pushing himself until he physically can't anymore. His symptoms could start to show during important meetings or tasks, creating a sense of drama and concern among his colleagues who don't know the real cause.
Perhaps Hermione uses her magic in an unconventional way that goes against what Rodolphus thought was possible. This could be in a situation where they are both facing a common enemy. Hermione's spell -casting creativity, like combining different spells to create a new and powerful effect, catches Rodolphus off -guard and makes him impressed.
The baby could be a half - demon, related to some other important character in the series. Maybe it's the offspring of a character Sesshomaru has some history with.
One way could be through a time - travel or alternate - reality plot. Maybe Hermione discovers a way to go back in time and change Severus' fate. She sees his potential for good and they form a deep friendship that gradually develops into a relationship where they consider having a child together. This would focus on their mutual understanding and respect for each other's intelligence and abilities.
One possible story could be that Kagome somehow finds an abandoned baby in the feudal era. Sesshomaru, being the powerful demon he is, initially shows little interest. But as Kagome tries to care for the baby on her own, Sesshomaru starts to notice her determination and kindness. Eventually, he might offer some form of protection to Kagome and the baby, perhaps out of a newfound respect for Kagome.
Well, one way could be through a magical portal that connects the wizarding world of Harry Potter to the feudal Japan world where Sesshomaru exists. Harry could inherit some of Sesshomaru's traits like his inhuman strength or his sense of pride. He might use his magic in a more combat - like way similar to Sesshomaru's sword fighting.
One way could be that Naruto jumps in front of a powerful attack meant for Haku. Maybe in a battle where Haku is protecting someone Naruto cares about, and Naruto's selfless nature makes him sacrifice himself. Then the story could focus on how the other characters react to Naruto's death, like Sasuke feeling guilty for not being there or Sakura being heartbroken.
There could also be humans who are afraid of the baby's mixed heritage. They might view it as an abomination and try to get rid of it. These humans could be part of a more superstitious group that believes demons and humans should never mix.
One possible plot could be that Sesshomaru, initially annoyed by the presence of the baby, gradually feels a sense of protectiveness. Maybe the baby has some special power or is related to an important prophecy. As he travels with the baby, he has to fend off various enemies who either want to harm the baby or use it for their own gain.
One way to develop the story could be focusing on the pregnancy. Momo might face difficulties due to her hero activities, and Izuku would be super protective. Then, after the baby is born, the story could show how they adjust to sleepless nights and diaper changes while still being heroes.