Maybe in this fanfiction, there is a threat that only the combined powers of Naruto and Midnight can stop. Naruto uses his shadow clones and Rasengan, while Midnight uses her Somnambulist quirk to put villains to sleep. Together, they form an unlikely but effective duo, and along the way, they learn about each other's worlds and values.
One possible plot could be that Naruto is somehow transported to the My Hero Academia universe. He meets Midnight and they team up to train students in a new, combined style of combat that incorporates Naruto's ninja skills and the quirks of the My Hero Academia world.
A plot could also involve Naruto being mistaken for a villain in the My Hero Academia world at first. Midnight is initially sent to capture him. But as she tries to subdue him, she realizes he is not a threat and instead has a unique set of skills. They then start to work together to help the heroes in My Hero Academia deal with a new type of enemy that is resistant to normal quirks, but Naruto's jutsu can handle.
Perhaps a powerful villain from the My Hero Academia world who is jealous of Naruto's power and wants to steal it for himself. He sees Naruto as a threat to his own plans of world domination and teams up with some of Naruto's old enemies from the Naruto universe to try and take him down. Midnight and Naruto then have to fight against this combined force.
A cool plot could be that Godzilla is actually an ancient being that was sealed away long ago in the My Hero Academia world. Due to some villainous activity, the seal is broken. Now, the heroes not only have to deal with the immediate threat of Godzilla but also figure out how to reseal it. There could be a sub - plot where a young hero discovers an old prophecy about Godzilla and has to convince the others that it's real and relevant to their current situation.
The OC could be from a different country and has a very different approach to heroics. Mina is intrigued by this and tries to learn more about the OC's culture and way of using their quirk. As they interact more, they start to collaborate on hero missions. Their relationship develops as they overcome cultural differences and work towards a common goal of protecting people in the My Hero Academia world. This would allow for exploration of different cultures within the context of the story.
One idea could be that the Pokemon world has some sort of villainous force that is affecting the balance of power, similar to the villains in My Hero Academia. The heroes from My Hero Academia are transported to the Pokemon world to help. They could team up with Pokemon trainers and use their quirks in combination with Pokemon attacks to fight against the common enemy.
One possible plotline could be a tournament - style event where characters from Naruto and My Hero Academia compete against each other. This would allow for exciting battles as the different powers and abilities are pitted against one another. For example, Naruto's shadow clone jutsu against Bakugo's explosions.
Well, it could be that Momo is transported to the Naruto world. She would be a bit out of place at first with her different abilities. But she quickly learns about chakra and how to use it in her own way. Maybe she creates some unique ninja tools with her quirk that help Naruto and his friends in a battle against a powerful enemy.
One possible plotline could be that Naruto mistakes a character from My Hero Academia as a threat to the ninja world. So, he banishes them to prevent any potential harm. For example, if he sees a powerful quirk user like All Might in the wrong context, he might think they are a new kind of enemy.
One possible plot could be that the heroes from My Hero Academia are transported to the Demon Slayer universe. They team up with the Demon Slayers to fight a new breed of demons that have quirks. Midoriya could learn some sword - fighting skills from Tanjiro and in return, Tanjiro could gain some knowledge about using quirks in combat.
One possible plotline could be about the next generation of heroes. Maybe the children of the current heroes are starting their own hero journey at UA High. They might face new villains with even more complex quirks.
A different idea is that some of the students from U.A. High School go on a field trip to Bikini Bottom. There, they learn about the different 'quirks' the underwater creatures have, like Sandy's ability to live underwater as a squirrel. And at the same time, they have to help SpongeBob and his friends with a problem, like stopping a giant sea monster that the normal underwater heroes can't handle. This would involve a lot of teamwork between the two groups.