One idea could be that Wanda Maximoff is transported to the Harry Potter universe. She could use her powers to help Harry and his friends during the Battle of Hogwarts. Her ability to manipulate energy and reality could give them an edge against Voldemort and his Death Eaters.
Another plot could be that both Harry and Wanda are brought to a neutral magical realm. There, they meet other magical beings from different universes. They have to figure out how to get back to their respective homes while also dealing with a power - hungry entity in this new realm that wants to steal their powers. Their combined magic and unique abilities would be crucial in this adventure.
One interesting plot point is how Wanda's powers interact with the magic in the Harry Potter world. For example, can her reality - warping abilities override powerful spells? Another is the cultural clash. Wanda comes from a different world, and seeing her adapt to the traditions and rules of Hogwarts is engaging. Also, the idea of her forming relationships with the characters. Will she befriend Hermione and learn from her vast knowledge? Or will she clash with Draco due to their different personalities?
One interesting crossover could be in a story where Wanda's magic interacts with the magic of the Harry Potter world in unexpected ways. For example, her chaos magic might disrupt some of the more structured spells in Hogwarts. Another could be a plot where Harry and his friends meet Wanda and they have to team up to fight a common enemy that is a threat to both their universes.
Another plot could involve Wanda accidentally getting trapped in one of Tony's experimental virtual realities. Tony has to enter the VR world himself to rescue her. Along the way, they learn more about each other's past traumas and form a deeper bond as they fight their way out.
There are likely some out there. You could start by looking on fanfiction platforms like Archive of Our Own. Search for crossovers between Harry Potter and Wanda Maximoff that are tagged as 'gen' (which usually means non - romantic/non - sexual). There might be some great stories that focus on their adventures together or how their powers could interact in a non - inappropriate way.
One idea could be a crossover where Harry Potter's magical world collides with the mutant abilities of Wanda Maximoff and Jean Grey. They could team up to fight a common enemy that threatens both the wizarding world and the mutant world. Maybe a dark sorcerer is trying to use mutant powers for his own evil deeds and they have to combine their skills to stop him.
One idea could be that a female Harry Potter discovers a time - travel spell and goes back in time to try and prevent Voldemort from ever becoming evil. She could try to befriend him as a child, show him kindness, and change the course of history. This would create a very different wizarding world and an interesting dynamic between the two characters.
One idea could be that a centaur saves Harry from a dangerous creature in the Forbidden Forest and then they form a bond. The centaur could teach Harry about the ancient magic that the centaurs possess. Another plot could be a centaur acting as a guide for Harry during his search for a rare magical herb that only grows in centaur - protected areas. They would have to work together to overcome various obstacles.
One idea could be that a Succubus is a new kind of magical creature discovered in the Forbidden Forest. The Hogwarts students and professors have to figure out how to deal with it, whether it's a threat or not. Another could be a Succubus who has lost her powers and comes to Hogwarts seeking help to regain them in a non - sexual way, like learning about different kinds of magic.
Well, a cool plot might be that Wanda accidentally creates a rift in time while trying to master her powers. She then has to team up with a younger version of herself to close the rift before it causes chaos across the multiverse. Or perhaps she forms an unlikely alliance with a villain from the Age of Ultron who has a change of heart. They then work together to stop a new, more powerful enemy that is emerging. Also, a story where she uses her powers to enter the minds of the Avengers and discovers their deepest fears and insecurities, which she then uses to strengthen their bond.
One plot idea could be that the male OC is a new Avenger and he and Wanda start off as friends. They train together and gradually develop feelings as they face various threats side by side. Another could be that the male OC has a special power that can calm Wanda's chaos magic when it goes out of control. This creates a unique bond between them. Or perhaps the male OC is from a different dimension and he and Wanda meet during a multiverse - related event and have to navigate their relationship while also dealing with the chaos of different universes colliding.