You can expect a variety of plots. It could be a plot where they meet and immediately form an alliance due to a shared threat. For example, a powerful dark force is looming over both of their worlds.
There are definitely some out there. Fanfiction writers love to explore crossovers between different game characters like Robin and Corrin. In some fanfics, their meeting is the catalyst for a much larger adventure. They might team up to face a common enemy that neither could defeat alone. Or it could be a more emotional story where they find kindred spirits in each other despite their different origins.
You can expect a unique take on the relationship between the two characters. It could explore their personalities in more depth, perhaps how they interact in different scenarios that aren't in the original game.
You can expect a focus on their relationship. It could be about their friendship, loyalty, and mutual respect. There may be elements of how they protect each other in the face of danger.
Well, typically in such fanfiction (assuming it's not adult - related), you might expect a more intense and perhaps angsty relationship exploration between Robin and Blackfire. It could involve their different personalities clashing or meshing in unique ways. Maybe there will be a focus on how they deal with their respective powers and how those play into their relationship.
Perhaps the plot will revolve around Sakura using her medical ninjutsu skills in a new and different way in the Anbu. She might be part of a special mission to uncover a conspiracy within the ninja village, and her knowledge and skills are crucial for the success of the mission. There could also be a sub - plot about her relationships with other Anbu members, either as friends or rivals.
We might expect to see Loki trying to fit in with the Avengers. He could start off as a reluctant member, perhaps forced to join due to some external threat. There could be a lot of tension as the other Avengers don't trust him at first. Then, as the story progresses, he might gradually earn their trust through his actions, like using his magic to save the day or providing crucial information about an enemy.
Well, we might expect a story where Naruko has to deal with the typical vampire struggles like controlling her thirst for blood. There could also be a plotline about her trying to hide her true nature from her friends or family. Maybe she falls in love with someone who is initially afraid of her vampire side.
Perhaps it will focus on Kuroko's extraordinary intelligence being applied to solve various problems. Maybe he uses his genius to outwit opponents in a game or come up with unique strategies.
Well, if it exists in a non - inappropriate way, perhaps the plot could involve Kallen somehow ending up in the Naruto world. Maybe she has some special abilities that the Naruto characters find fascinating. And there could be a plot around her adjusting to this new world while also having some sort of relationship, either friendly or something more, with Naruto characters.
Well, we could expect a lot of culture clash. Grimmjow is from a world of Soul Reapers and Hollows, which is very different from the magical world of Harry Potter. Maybe Grimmjow could end up at Hogwarts and cause chaos among the students and teachers. He might not understand the rules of magic and end up using his own powers in unexpected ways.