Maybe Superman could be a mentor figure. He has so much experience and his values could influence the characters in My Hero Academia. For example, his strong sense of justice could inspire Deku even more. He could teach the students about using their powers responsibly in a different way compared to the local heroes.
Well, Wolverine could fit into the My Hero Academia storyline as a foreign hero or a special guest. His mutant powers would be seen as a very unique form of 'quirk' in the MHA world. He could be brought in to train the students at UA, sharing his combat experience which is far different from what they usually get. Maybe he could be part of a special international hero exchange program.
In a My Hero Academia fanfiction, Gohan could be seen as a hero from another dimension. His moral code, which is similar to the heroes in MHA, would make him a natural fit. He could also train the students in new ways of combat, using his martial arts skills combined with his Saiyan abilities.
Sakura Haruno might enter the MHA universe through some sort of multiverse portal. Once there, her strong - willed and determined nature would make her a great hero - in - training. She could learn to use her physical strength, which she had developed in the Naruto world, in combination with a new MHA - style quirk. For example, she could have a quirk that enhances her strength even further when she focuses her chakra (or a similar energy concept in MHA). This would make her a formidable force against villains.
She could be a transfer student from another hero academy with her own set of unique skills. Her powers would likely make her stand out among the MHA students.
One way it could fit is by having a character with a quirk that allows them to mimic the Sharingan's abilities. For example, they might be able to copy other heroes' or villains' quirks in a similar way to how the Sharingan can copy jutsu in Naruto. This would add a whole new level of strategy and intrigue to the My Hero Academia world.
Well, Goku's super strength and his ability to constantly power up could be a huge asset in the My Hero Academia fanfiction world. He could be like an otherworldly hero with his Saiyan powers. His Kamehameha wave would be an extremely powerful quirk - like ability. Maybe he could be a visiting hero from another dimension, coming to help out in the battles against the villains in the My Hero Academia universe.
Well, one way could be that Ichigo arrives in the My Hero Academia world through some sort of interdimensional portal. His powers, like his Soul Reaper abilities, would be seen as a very unique and powerful quirk. He might end up at UA, either as a student or a guest instructor. His strong sense of justice would align well with the values of the heroes in that world.
In fanfiction, Broly might be a villain who comes to the My Hero Academia world seeking a worthy opponent. His raw power would pose a huge threat to the heroes, and they'd have to figure out how to stop him without getting killed.
Well, one way could be that his alchemy skills are seen as a unique quirk. He might attend UA and struggle to adapt to a world where heroics are more about using superpowers rather than alchemy. For example, he could have a hard time during combat training because his methods are so different from the typical quirk - based attacks.
Gohan could fit in by being a transfer student. His Saiyan powers would be seen as a very unique 'quirk'. In the harem aspect, his kind heart would draw the attention of the female characters. For example, Mina would find his positive attitude infectious.