A third storyline could be that Android 18 is sent by the Red Ribbon Army remnants to spy on Master Roshi. But as she spends time with him and his students, she starts to question her loyalties. Roshi, sensing something is off, tries to reach out to her. Eventually, she defects from the Red Ribbon Army and becomes a true defender of Earth, learning martial arts from Roshi along the way.
The fanfic could also revolve around a mission. For example, there's a new threat in the Dragon Ball universe and Android 18 and Master Roshi team up to face it. Along the way, they have to overcome their differences. Android 18's cold - blooded nature (initially) clashes with Roshi's more laid - back and traditional approach, but eventually they find a way to work together effectively.
One interesting interaction could be when Android 18 challenges Master Roshi to a sparring match. Roshi, despite his age, shows some unexpected moves which surprises Android 18. This could lead to her respecting him more.
Well, in canon, they don't really interact much. In a fanfic, their interaction could be full of surprises. For instance, Android 18 might be much more brash and direct towards Roshi compared to how she behaves with other characters. Since she's an android, she may not have the same respect for Roshi's age - old traditions right away.
In a fanfiction, the female android might be on a mission to destroy Gohan at first. But as she gets to know him, she realizes that he is not the enemy she thought he was. Gohan, in turn, tries to show her the value of life and friendship. Their relationship then transforms from enmity to a strong alliance.
One creative storyline could be where the characters from Batim end up in the Underground of Undertale. Maybe Bendy and his crew are mistaken for strange monsters by the Undertale characters at first. They then have to navigate through the various areas of the Underground, facing challenges like the puzzles in the ruins or the battles in Snowdin, all while trying to find a way back to their own world. Another idea is that the Ink Machine from Batim somehow gets connected to the Determination power in Undertale, causing all sorts of wacky and unexpected interactions between the two universes.
One creative storyline could be Optimus Prime finding a lemon - like energy source that has strange powers. This could lead to a whole new adventure where he has to figure out how to use or contain it without it causing chaos. Maybe the lemon - like energy source attracts some new, unknown enemies.
Perhaps a crossover where the villains from both universes team up. Salem from RWBY and Dio from Jojo could form an alliance. The heroes from both RWBY and Jojo would then have to put aside their differences and work together. This would bring in all sorts of interesting dynamics, like the different fighting styles and power sets having to mesh in order to take on this super - powerful villainous alliance.
Android 18 in a fanfic with Roshi could be a source of conflict or resolution. She might initially be at odds with Roshi due to her android nature and his more traditional ways. But as the story progresses, they could find common ground. Maybe she has a mission that Roshi unknowingly gets involved in, and together they have to face various challenges, which in turn builds an unexpected friendship or partnership.
Roshi could be depicted as a comical yet endearing character in relation to Android 18. He might be constantly amazed by her android abilities, like her super strength or energy blasts. At the same time, he tries to impress her with his own martial arts skills, which might seem a bit primitive compared to her technology - based powers, but still hold a certain charm and wisdom.
A really interesting fanfic idea could be set in a post - apocalyptic version of the Dragon Ball universe. Android 18 and Krillin have to fight to protect the few remaining survivors. They use their unique skills, with Android 18's android powers and Krillin's martial arts. Their relationship becomes a source of hope for those around them, as they prove that love can still exist even in the harshest of times.