Another plot could be a battle scenario. Android 21, with her combat abilities, gets into a fight with Naruto. Naruto initially struggles because he's not used to her style of fighting. But as the battle progresses, he starts to figure out her weaknesses and uses his ninja skills like shadow clones to outmaneuver her. In the end, they might respect each other's strength and start to cooperate.
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.
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.
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 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 possible plot could be a crossover battle. Naruto, with his powerful ninja skills like Rasengan and Shadow Clone Jutsu, could face off against Majin Android 21's unique abilities. Maybe they start off as enemies but then realize they have a common foe. For example, an evil entity that threatens both their worlds. Naruto could use his determination and leadership skills, while Majin Android 21 could bring her combat and energy - based powers to the table. In the end, they might combine their forces and develop a new friendship or alliance.
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.
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.
Another fanfiction concept could be that female Android 17 has been sent to the Naruto universe by some unknown force. Naruto, being the curious and friendly ninja he is, tries to befriend her. He shows her the ways of his village, and she in turn teaches him some of her combat techniques, leading to an interesting exchange of cultures.
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.