A great plot idea would be that Ash and Android 21 are brought together by some sort of time - traveling anomaly. They then have to find a way to get back to their respective worlds. Along the way, Android 21 starts to develop a fondness for Ash's Pokémon. And Ash, in turn, helps Android 21 deal with her inner demons from her past as a villain. This could involve a lot of character development for both of them as they face various challenges in this strange new situation.
One plot idea could be that Ash and Android 21 team up to fight a common enemy in a tournament. Another could be a story where Android 21 tries to understand human emotions through Ash's experiences. Or perhaps a plot where they travel through different dimensions together.
One idea could be Android 21's struggle to fit into a world that fears her. She has to prove that she's not a threat and tries to make friends. Another could be her discovery of new powers and how she uses them for good. Maybe she teams up with other characters to fight a common enemy.
One idea could be a story where Gohan and Android 18 team up to protect the Earth from a new, powerful threat. They start off as reluctant allies but gradually develop a deep respect for each other's abilities. Another plot could be a time - travel story where they go back in time and have to prevent an event that changes their future relationship. Maybe they end up having to work together to stop a younger version of Cell from evolving further.
A great plot idea would be Android 21 crossing into a world where technology is feared. She'd have to prove that not all advanced technology is bad. Also, she could cross into a world of pirates, using her skills to navigate the high seas and fight off other pirates.
One plot idea could be Android 17 in a post - apocalyptic world, using his powers to protect the few remaining humans from other threats. Another could be Android 17 getting transported to an alternate universe where he has to team up with his evil self to defeat a greater enemy. Maybe he could also have a story where he tries to integrate into human society and discovers emotions he didn't know he had.
One idea could be that Android 21's unique powers attract the attention of Naruto. He might see her as a new kind of challenge. Maybe she has some sort of energy that is similar to chakra in a way. And Naruto tries to understand her and her powers, leading to an unexpected friendship.
Maybe in the fanfiction, Android 18 gets injured while protecting Gohan from a new powerful enemy. Gohan then takes care of her and in that time of vulnerability, they realize their feelings for each other. This could lead to them exploring a relationship while also trying to figure out how to defeat the enemy that still lurks.
One idea could be that the OC is a scientist who is intrigued by Android 18's unique blend of power and humanity. He tries to find a way to make her more 'human' in terms of emotions, leading to a series of adventures where they face various threats together. Another could be that the OC is a time - traveler who accidentally lands in the Dragon Ball universe and forms an alliance with Android 18 to prevent a catastrophic event in the future. And a third idea might be that the OC is a martial artist who challenges Android 18 to a series of battles, which gradually turn into a friendship and then something more romantic as they learn about each other's values.
One idea could be Ash traveling to a new, mysterious region full of never - before - seen Pokémon. He could encounter a powerful and rare Pokémon that becomes his new partner. Another could be Ash getting lost in a time - warp and having to find his way back while also learning about the past of the Pokémon world.
Another plot could be that Ash enters a high - stakes Pokémon tournament in Cynthia's region. Cynthia becomes his mentor, teaching him advanced strategies, and they develop a strong friendship along the way.
One idea could be Ash and Togepi getting lost in a mysterious forest. They encounter strange new Pokémon and have to work together to find their way out. Another plot could be Togepi getting sick and Ash having to search for a rare herb to cure it. He meets different trainers along the way who either help or hinder his quest.