Maybe there could be a quirk - semblance exchange. A character from My Hero Academia could temporarily gain a RWBY character's semblance and vice versa. This would lead to some really cool and unexpected battle combinations. Like Deku having Ruby's speed semblance for a while and using it in a creative way during a fight.
One great 'My Hero Academia' crossover fanfiction is the one where they cross over with 'One Piece'. It combines the unique powers of the 'My Hero Academia' world with the adventurous and diverse world of 'One Piece'. The characters interact in really interesting ways, like Midoriya being amazed by Luffy's Devil Fruit powers and Luffy being intrigued by the concept of Quirks.
One idea could be that Kakashi is somehow transported to the My Hero Academia world. He could become a teacher at UA, using his ninja skills and wisdom to train the students in new and unique ways. His Sharingan would be a very interesting power in the MHA universe.
One idea could be that Godzilla arrives in the My Hero Academia world during a major villain attack. The heroes initially see Godzilla as a threat but soon realize that he is targeting the same villains who are causing environmental destruction. His massive size and power could be a game - changer in the battle.
Uraraka and Blake could be an interesting team - up. Uraraka's zero - gravity quirk could be used in some really creative ways to help Blake in her stealthy attacks. Blake could teach Uraraka some of her ninja - like combat moves and they could work together to take on enemies that are difficult to reach or overpower.
A great crossover idea is with the Dragon Ball series. The powerful Saiyans could interact with the My Hero Academia characters. Goku could train the students at UA to reach new levels of power. Also, a crossover with the Attack on Titan world would be intense. The heroes would have to deal with Titans in a whole new way and use their quirks in that battle - filled environment.
Another common theme is the formation of new alliances. Since it's a crossover, 'eraserhead my hero academia rwby fanfiction' often shows Eraserhead and characters from both universes forming new teams or partnerships. They combine their skills and powers to overcome challenges that neither could face alone, which is really exciting to read about.
One interesting crossover could be the characters from My Hero Academia and RWBY teaming up for a big battle. For example, Izuku Midoriya's unique quirk combined with Ruby Rose's scythe - wielding skills would make for an epic fight scene. They could be facing a common enemy that has the characteristics of both the Grimm from RWBY and the villains in My Hero Academia.
Bakugo Katsuki and Yang Xiao Long is also a fairly common pairing. Their hot - tempered personalities can create a lot of interesting interactions. They are both strong - willed and powerful fighters, and their clashes and potential romances are explored in some fanfictions.
Here's a simple start for a 'prototype My Hero Academia crossover fanfic': In a world where the quirks of My Hero Academia exist alongside the powers from 'prototype'. Alex Mercer finds himself in the middle of Musutafu city. He's confused by the sight of people with all these strange abilities. Izuku Midoriya spots this strange man and approaches him. Mercer, being the shape - shifter he is, tries to blend in but his lack of knowledge about quirks starts causing some misunderstandings. As they interact, Mercer realizes that these 'quirks' could be a new form of power to study, while Midoriya is both fascinated and a bit scared of Mercer's abilities.