One great 'Haikyuu! Bnha Crossover Fanfic' is 'Volleyball Heroes'. It combines the unique powers from Bnha with the exciting volleyball matches of Haikyuu. The characters' interactions are really interesting, like when Midoriya tries to learn volleyball techniques from Hinata. It's a fresh take on both universes.
First, you need to be familiar with both universes. Know the characters, their personalities, and the rules of each world. For example, in Haikyuu, understand the volleyball strategies and the different teams. In Bnha, know the quirks and how they work. Then, think of an interesting concept for the crossover. Maybe it could be about the Bnha characters joining a volleyball tournament in the Haikyuu world.
In a Haikyuu fanfic featuring Sakura Haruno, it could be really interesting. Maybe she could be a manager for one of the volleyball teams, bringing her own unique skills from the Naruto universe like her medical knowledge to help with the team's injuries. It would add a whole new dynamic to the story.
One idea could be a crossover with Harry Potter. Imagine Deku attending Hogwarts and learning magic while also trying to control his One For All quirk. He could make friends with Harry and they could share their experiences of being the 'chosen ones'.
The cultural clash. BNHA has a modern, superhero - like society with hero agencies and rankings, while Undertale has a more fantasy - based, underground world with its own set of rules and moralities. In a crossover fanfic, seeing how the characters from each world adapt to the other's culture is really interesting. It can lead to some really fun and thought - provoking situations, like how the BNHA heroes would deal with the monster - human relationships in Undertale.
I really liked 'BNHA: Undertale Edition'. In this fanfic, the author does an amazing job of transplanting the BNHA characters into the Undertale universe. They face off against the classic Undertale foes but with their own BNHA - style abilities. It's full of action - packed battles and some really heartwarming character interactions.
The most interesting part is seeing the different power systems interact. Nen from HxH and Quirks from BNHA are so different. For example, how would Gon's Jajanken deal with a villain's powerful Quirk? It creates a lot of unique battle scenarios.
First, decide which two universes you want to cross over. Then, think about how the characters from each universe will interact. For example, if it's a Bnha and Pokémon crossover, you could think about which Pokémon a character like Ochaco would have. Just start with a simple idea and build on it.
I really liked 'Haikyuu at Chaldea'. In this fanfiction, the Haikyuu characters end up in the FGO world. The author does a great job of showing how the Haikyuu team members adapt to the strange new environment filled with magic and Servants. They bring their own team spirit and determination, which has an impact on the events in the FGO world.
A third plot idea might be that there is a strange phenomenon that swaps some of the players' abilities. So a Haikyuu player suddenly has the ability of a Kuroko no Basuke character and vice versa. This would lead to a lot of confusion but also some really interesting match - ups as they try to adapt to their new - found skills.