A more complex plotline could involve time - travel. Pyro's sister could travel back in time to prevent Pyro from making certain bad decisions that led him down a dark path in the X - Men universe. This would involve her interacting with different versions of the X - Men characters and changing the course of events.
You can try searching on fanfiction websites like Archive of Our Own (AO3). It has a large collection of X - Men fanfics. Just type in 'X Men Pyro Sister' in the search bar, and it will show relevant stories.
In a 'superman in x - men harem fanfic' plotline, Superman could be on a mission that intersects with the X - Men's world. His presence disrupts the normal dynamics among the X - Men, especially among the female members. They vie for his attention, and he has to balance his newfound relationships while also helping the X - Men with their long - standing issues like mutant - human relations. There could also be a love triangle or multiple love triangles among the X - Men female characters and Superman, adding more drama to the story.
One possible plotline could be that Karma's sister discovers the truth about the classroom and decides to join in on the assassination attempts, adding her own skills and strategies. Another could be that she tries to convince Karma to leave the dangerous situation.
Perhaps it could be a story where Seventh Sister has a change of heart. She starts to question her loyalty to the Empire after encountering Luke. Luke, in turn, tries to convince her to turn to the light side. They go on a journey together, and along the way, they face various challenges that test their new - found alliance.
A possible plotline might be that a dark wizard is after Hermione because of her new - discovered connection to the Malfoys. Draco, feeling a sense of family loyalty despite their differences, decides to protect her. Along the way, they learn more about their family's past and the reasons behind Hermione being separated from them. It could also involve Hermione trying to reconcile her Gryffindor values with the Slytherin - like values of the Malfoy family. There might be a scene where they have to face their parents together, and the Malfoy parents have to accept Hermione as their daughter, which would be a huge shift in their pure - blood ideology.
The fanfic could also explore her relationships outside the family. She might fall in love with someone who is not part of the Sohma world. This would bring a whole new set of challenges as she has to balance her love for this person and her loyalty to her family. There could be a lot of drama as she tries to keep her relationship a secret or convince her family to accept it.
A really interesting Pyro x Scout fanfic I've read is 'Flames and Speed'. This fic delves deep into how they might interact on a daily basis in the TF2 universe. It has some really cool action scenes as well as some heart - warming moments between them.
One possible plotline could be the OC using her knowledge of the Naruto universe to prevent certain tragedies from happening to Itachi and his family. For example, she might try to stop the Uchiha massacre.
In the X-Men comic, Pyro is often associated with the team's battles and storylines. His abilities make him a valuable asset or sometimes a source of conflict within the group. Also, his character development is closely tied to the mutant themes explored in the comic.
Pyro X-Men comics often feature intense battles and power showcases. The characters have complex personalities and relationships.