Midoriya from 'My Hero Academia' is also an interesting choice. Imagine him being mentored by Tohru in some aspects of using power. Since Midoriya is always eager to learn and improve, Tohru could teach him about different ways of controlling and using strength, which could be very different from what he's used to in his own world.
Deku would be really interesting. He has such a complex journey in the original series. If he's deaged, he'd have to relearn all the things he's worked so hard to master. His relationship with his quirk, One For All, could be explored in a new way. Maybe he'd struggle more with controlling it as a deaged version. Also, his relationships with his friends and teachers, like All Might, would be different. He'd be more naive and inexperienced, which could create some really engaging storylines.
Todoroki from My Hero Academia could be really interesting. His dual - quirk nature could have some really cool interactions with the ghoul powers. He could use his ice side to counter the heat - based attacks of some ghouls, or his fire side to fend off cold - blooded ghouls. His complex backstory could also add depth to a story set in a crossover world.
Uraraka could also be a great focus. Her ability to make things float could have some really unique applications in Wonderland. She might befriend some of the floating objects or creatures there. Also, her kind heart could lead her to try and help the downtrodden characters in Wonderland, like the Dormouse, and in the process, she could learn more about herself and her quirk.
One idea could be a crossover where the characters from 'My Hero Academia' attend a festival in the world of 'Dragon Maid'. They could interact with Tohru and the other dragon maids, leading to humorous and heartwarming moments. For example, Midoriya might be amazed by the dragons' powers and try to learn from them in his own clumsy way.
Bakugo would be really interesting. His hot - headed nature could lead to some hilarious situations at the beach. Maybe he gets frustrated with the sand getting in his shoes or is overly competitive during beach games.
Midoriya is always a great choice. In an alternate universe, say he never met All Might and didn't inherit One For All. He might have to find his own way to be a hero, perhaps by developing a unique quirk - enhancing technology. This would show his determination in a different light. Also, an AU where Midoriya is a villain could be fascinating. We could see how his intelligence and analytical skills would be used for evil, which would be a complete contrast to his usual heroic self.
One common theme is friendship. Just like in the original works, the fanfictions often explore how characters from 'My Hero Academia' and 'Dragon Maid' form strong bonds. For example, the heroes might befriend the dragons and learn about their unique cultures.
I think Deku would be really interesting. He could be sharing his thoughts on how he's constantly trying to improve his quirk and live up to All Might's legacy. His nervous but determined personality would add a lot of charm to the sleepover.
Reincarnating as Midoriya Izuku before he gets One For All would be a great choice. You could then explore different ways he could have become a hero without inheriting that quirk. He could develop his own unique fighting style based on his intelligence and analysis skills. Also, reincarnating as Todoroki Shoto and changing his relationship with his father from the start, perhaps leading to a more harmonious family and a different kind of hero development for Todoroki.
I think Ruby would be a great choice. Her innocence and determination in RWBY could be an interesting contrast to the often more battle - hardened and power - hungry characters in Dragon Ball. She could learn a lot from them about power and also teach them about the importance of friendship and teamwork in a different way.