One way to develop it is through the exploration of relationships. Harry could form a special bond with each Avenger. For instance, he might see Thor as a kind of magical being from another realm like some wizards in his world. With Black Widow, he could share his experiences of having a difficult past and how they overcame it. This would build a deep emotional connection among them.
The story could develop with Fem Harry Potter being a sort of wildcard in the Avengers. Her background in the wizarding world gives her a different perspective. She might initially struggle to adapt to the high - tech environment but then find ways to combine magic and technology. For instance, she could use a spell to enhance the power of Captain America's shield. And her experiences with dark magic could help the Avengers better understand and combat otherworldly threats that they haven't faced before.
Some of the Avengers would be very protective. Captain America would see Harry as a kid in need of guidance and safety, just like he does with his teammates. Tony Stark might be initially skeptical but would soon see the potential in Harry's magic. Thor would probably be fascinated by Harry's magical powers and see him as a worthy addition to their group.
To develop it, you could introduce a new character who is a hybrid of a wizard and a Cybertronian. This character could be the link between the two worlds. Harry could then be drawn into the Cybertronian world through this character. In the Cybertronian world, Harry could discover that magic has a different manifestation. He could learn to combine his magic with the technology of the Cybertronians. For example, he could use his wand to control the energy flow in a Cybertronian's body, or use a spell to enhance a Cybertronian's weapon. The story could also explore the ethical implications of mixing magic and technology, and how it affects both the wizarding world and the Cybertronian society.
Harry Potter might save the Avengers by using his magic to teleport them away from danger. He could use Apparition or the Floo Network if he could somehow make it work in the Avengers' world.
Harry Potter could lead the Avengers through his strategic thinking. He's had to plan against Voldemort and his Death Eaters. So he could come up with battle plans for the Avengers. He might use magic to communicate with the team over long distances, like a modified version of the Floo Network. Also, he would encourage the Avengers to embrace their individual strengths, just as he did with his classmates at Hogwarts.
He could use his invisibility cloak for stealth missions with the Avengers.
Well, Harry Potter might assist the Avengers in fanfiction by providing unique forms of transportation. His ability to apparate or use the Floo Network could be a great advantage for the Avengers. Also, his experience in fighting dark magic could give the Avengers new strategies against their powerful foes.
One way could be that a magical portal opens between the two universes and Harry accidentally stumbles into the Nilfgaardians' territory. Then he has to fight to defend himself. Another idea is that some dark magic force brings the Nilfgaardians to Hogwarts and Harry steps up to protect his school and friends.
One way is to start with a magical accident or a powerful spell that transports Harry into the Witcher universe. Once there, he could be found by an old Witcher who takes him under his wing. They start training him, and Harry slowly learns the ways of the Witcher.
The story could also explore the reactions of the animal kingdom to this strange adoption. Other lions might be confused or even hostile towards the lioness for taking in a human. Meanwhile, the human community might be in shock when they discover the child is being raised by a lioness. They would have to decide whether to try and rescue the child or let nature take its course.