Well, perhaps a plot where Genos follows Saitama into the My Hero Academia world. Genos could enroll in UA as well and show off his advanced technology - based powers. He might get into a competition with Bakugo over who is more powerful. Meanwhile, Saitama is just casually wandering around, accidentally solving problems and leaving the students and heroes in awe of his effortless strength.
Maybe there's a device that accidentally transports the top heroes from both universes together. In this crossover, All Might and Saitama could have a friendly competition to see who can defeat the most villains in a day. However, they quickly realize that their worlds have different threats and they need to work together. For example, Saitama could learn about the concept of 'quirks' and how it affects hero society, while All Might could be amazed by Saitama's pure physical strength.
One idea could be a crossover where Saitama ends up in the My Hero Academia universe. He might accidentally enroll in U.A. High School. His overpowered abilities would shock everyone, and he could end up being both a mystery and an inspiration to the students. Another plot could be about Deku getting some training from Saitama. Saitama's unique training methods might give Deku a new perspective on how to use his power.
One idea could be a crossover where Saitama from One Punch Man ends up in the My Hero Academia world. He could participate in the hero school entrance exam and completely shock everyone with his overwhelming power. His nonchalant attitude towards heroics might also rub off on the students in a funny way.
Maybe a story where the heroes from Boku no Hero Academia are faced with a villain so powerful that they have to seek the help of Saitama. It would be interesting to see how they interact with his nonchalant attitude towards heroics.
One idea could be a crossover with Dragon Ball. Saitama could participate in the World Martial Arts Tournament and effortlessly defeat all the opponents, creating a hilarious situation. His nonchalant attitude would contrast sharply with the intense and competitive nature of the Dragon Ball characters.
One idea could be that Naruto characters are transported to the My Hero Academia world. Naruto himself could be seen as having a very unique quirk, like his chakra manipulation could be considered a superpower. They could team up with the students of UA to fight against a common enemy, like a group of villains who are after the secrets of chakra. Another plot could involve the My Hero Academia characters traveling to the Naruto world and learning about ninjutsu and how it differs from their quirks.
One idea could be that Ladybug's Miraculous powers are somehow connected to a Quirk in the My Hero Academia world. For example, maybe her Lucky Charm ability could be seen as a very unique and unpredictable Quirk. Another plot could involve Ladybug and a My Hero Academia character teaming up to fight a common enemy that is causing chaos in both their worlds. This would require them to learn about each other's powers and work together in a way that combines the best of both universes.
One idea could be a crossover with the Harry Potter universe. Imagine Deku going to Hogwarts and learning magic while also using his Quirk. He could make friends with Harry and they could learn from each other's skills. Another idea is a crossover with the Avengers. The heroes from My Hero Academia could team up with the Avengers to fight a common, super - powerful enemy. Maybe All Might and Captain America could have an interesting conversation about leadership and heroism.
One idea could be that Naruto and Saitama somehow end up in a shared dimension where they have to team up to defeat a common enemy. For example, a powerful demon from Naruto's world that has the ability to regenerate like some of the monsters in One Punch Man's world. Another plot could involve Naruto learning Saitama's training regime and trying to incorporate it into his own ninja training, while Saitama is intrigued by Naruto's chakra system and tries to figure out if he can use it to make his punches even more powerful.
Genos' robotic enhancements and Kirishima's hardening quirk could create an interesting combination. Genos could provide Kirishima with some technological upgrades to his hardening ability, making him even more indestructible. On the other hand, Saitama's speed could be combined with Iida's engine quirk to create a super - fast movement ability that could outpace almost any villain.