One idea could be a story where Goku and Kefla have to team up to face a new, powerful enemy that neither could defeat alone. They start off not trusting each other much, but as they fight side by side, they learn to respect one another's strength and fighting styles.
One idea could be that the OC is a powerful warrior from a different dimension. They meet Kefla during a universal tournament. Their powers are so different yet complementary that they start to train together, and gradually a deep bond forms between them as they learn from each other's fighting styles.
Sure, there are quite a few. These fanfictions often take the strong and unique personalities of Goku and Kefla and weave them into a romantic narrative. Some might be more action - packed with their love story developing in the midst of battles and challenges, while others could be more about the quiet, tender moments between them. It really depends on the creativity of the author.
One idea could be a crossover where Goku somehow ends up in the RWBY universe. He could train the RWBY characters, sharing his martial arts knowledge and helping them improve their combat skills. For example, he could teach Ruby how to better control her speed and use her scythe more effectively in combat.
One idea could be a fanfiction where Kefla has to team up with Goku and Vegeta to face a new, extremely powerful enemy that is threatening the entire universe. This would explore how she would interact with them on a more equal footing outside of a fight - to - the - death scenario. Another idea is a story about Kefla's life on her home planet before coming to Earth and her training there.
One idea could be that Goku and Goku Black are forced to team up against an even greater threat from another universe. They start to understand each other's fighting styles during the battle and gradually develop a grudging respect for one another.
In some versions, the female Goku could be part of a prophecy. The two Gokus meet, and at first, there is some confusion and misunderstanding. But as they get to know each other, they discover that they are key to fulfilling the prophecy. They combine their powers and defeat an ancient evil that was threatening both of their worlds.
You can expect a lot of creativity. Since it's fanfiction, the authors can play around with the characters' personalities and the Dragon Ball universe rules. Maybe Goku shows a more romantic side that we don't often see in the original series, and Kefla could be softened in some ways to fit the love story.
One common theme could be the power dynamic between Goku and Kefla. Since they are both very powerful characters in the Dragon Ball universe, exploring how their powers interact and complement each other might be a theme. For example, in battles or training sessions.
I'm not sure about a specific 'goku x kefla fanfic' to recommend. You could try searching on fanfiction websites like Archive of Our Own or FanFiction.net. There might be some interesting ones there.
One idea could be a crossover universe where Goku somehow ends up in the Naruto world and meets Sakura. They could team up to fight a new common enemy that is causing chaos in both their worlds. Maybe this enemy has the ability to steal energy like the Saiyans but also uses genjutsu like the ninjas.