One idea could be an OC with a unique power that can nullify the energy of any attack, which throws off the Saiyans' fighting strategies. Another could be an OC who is a master of a long - forgotten martial art that gives them an edge in battles against the Z - fighters. Maybe an OC who has a connection to an ancient and powerful race that even the Kais don't know much about.
One idea could be an OC with a unique ki ability that no one in the Dragon Ball Z universe has seen before. For example, the ability to transform into an energy form that can pass through solid objects. Another plot could involve an OC who is from a long - lost race in the Dragon Ball Z lore and has to find their place among the Saiyans, Namekians, etc. A third idea might be an OC who is a time - traveler and has to prevent a major catastrophe in the Dragon Ball Z timeline.
For a Beerus OC in fanfiction, it could be an OC who was once a normal cat - like creature on a destroyed planet. Beerus, out of pity or some unknown reason, bestowed some of his power on this creature. As a result, the OC gradually evolved into a powerful being with some of Beerus's characteristics. This OC could have a very different personality from Beerus, being more kind - hearted and using their power to help revive planets rather than destroy them.
One interesting plot could be a new villain emerging from a long - forgotten dimension. This villain has powers that are a mix of different techniques from all the universes in Dragon Ball. He starts causing chaos by stealing the energy of strong fighters to open a portal to an even more powerful realm.
Another interesting plot could be that the gamer aspect brings in virtual reality elements. The Z - fighters enter a virtual world where they have to fight enemies with different rules. This virtual world could have power - ups and obstacles that are based on video game concepts, like finding hidden keys to unlock new areas or defeating bosses to gain special abilities that they can then use in the real Dragon Ball Z world.
One idea could be a crossover with the Naruto universe. Goku and Naruto could team up to fight a common enemy. Maybe they face an evil villain who has the power - stealing abilities like Cell and the ability to use powerful ninja jutsus. Another plot could be a crossover with One Piece, where Luffy and Goku have a friendly competition about who can eat more food and then end up having to work together to defeat a new threat at sea that has the strength of Saiyans and the deviousness of pirates.
Perhaps a fanfiction where a young Saiyan from a destroyed planet manages to find their way to the Xenoverse 2 world. This Saiyan has a different fighting style compared to the ones we know. They join the Time Patrol not just to save timelines but also to find a new home for their kind. Along the way, they face discrimination from some of the other races in the Xenoverse due to their Saiyan heritage, but they prove themselves worthy through their strength and determination.
The Saiyan OC could be a time - traveler who comes to the Dragon Ball Z era. Android 18 meets this strange Saiyan and at first is suspicious. But as they get to know each other, they realize they can work together. They might have to deal with the chaos that the Saiyan OC's time - traveling has caused in the timeline. Maybe some old villains are resurrected because of it, and Android 18 and the Saiyan OC must find a way to stop them while also dealing with their own relationship development.
One idea could be Goku Jr facing a new, powerful enemy that has a unique power related to time manipulation. This would force him to train in ways he never has before and seek help from unexpected allies, like some of the older, wiser characters from the original Dragon Ball Z series.
Well, a plot could be Android 21 somehow getting her hands on the Namekian Dragon Balls. Since she has that scientific mind, she might try to figure out how to modify the wishes. In the process, she could draw the attention of Frieza who wants the Dragon Balls for his own evil purposes. Then the Z - fighters would have to step in to protect Android 21 and the Dragon Balls. Another plot idea is that Android 21 is from an alternate universe where she was created by the good guys. When she crosses over to the main Dragon Ball Z universe, she has to adjust to the different power levels and politics among the characters. And she could end up being a key player in the fight against Buu, perhaps using her unique abilities to weaken Buu in some way.
One idea could be Goku and Gohan going on a special training journey to a new planet with unique gravity and energy sources. This would force them to adapt and develop new techniques together.