An interesting plot could be that the OC is the last of the Frieza race after a great catastrophe. They are on a mission to rebuild their race but in a more benevolent way. However, other races are suspicious of their intentions, and they have to prove themselves worthy of trust.
One way to create a Frieza Race OC for Dragon Ball Z fanfiction is to first think about their physical appearance. They could have the signature purple skin, white horns, and long tails like Frieza. For their personality, maybe they're more cunning and strategic than the average Frieza Race member. They could be an outcast who doesn't agree with the cruel ways of their race and is secretly trying to find a way to change their people's nature. Their power level could start off relatively low but through various adventures in your fanfiction, they grow stronger and learn new techniques.
You can start by having the Frieza Race OC show up during a battle. For example, when the Z - Fighters are fighting some of Frieza's minions, the OC could arrive and seem like they're on the side of the minions at first. But then, they turn on their own kind because they see the unjust nature of the fight. This would create an interesting twist in the plot.
One interesting plot idea could be that Frieza somehow manages to gain new powers on a distant planet and returns to challenge Goku again. But this time, instead of just brute strength, he uses cunning strategies. Another could be a scenario where Goku and Frieza are forced to team up against an even greater threat from another universe. This would be a great chance to explore their complex relationship.
One interesting storyline could be a female Frieza race character trying to redeem her race's bad reputation. She could go on a journey to help planets in need, much like Goku and his friends do. Another could be her getting involved in a power struggle within the Frieza race, where she has to use her wits and new - found powers to survive.
Power and dominance are common themes. Since the Frieza race is known for being powerful, many fanfictions explore how members of this race strive for more power or try to maintain their dominance. Another theme is revenge. For example, a surviving Frieza race member seeking revenge on those who defeated Frieza.
I really like 'A Frieza Race Warrior's Journey'. In this fanfiction, it focuses on a young Frieza race member who tries to break free from the traditional ways of his race. He wants to find a new path that doesn't involve all the destruction and tyranny that the Frieza race is known for. It has some great action scenes and character development.
Perhaps an OC that is a powerful wizard in the Dragon Ball universe. This wizard OC discovers a dark magic that is threatening to consume the universe. They must then seek the help of the Z - fighters, who are initially skeptical of magic. The OC has to convince them of the danger and together they find a way to stop the dark magic. Along the way, the OC teaches the Z - fighters about the power and responsibility of magic.
A believable Frieza race OC can be created by adding depth to their relationships. They could have a mentor from another race who taught them different values. Their relationships with other Frieza race members can also be explored. Are they an outcast? Do they have friends within the race? By building these relationships and showing how they affect the OC's actions and decisions, the character will become more believable in the context of the fanfiction.
Some writers show the Frieza race's culture as being very hierarchical. There's a clear pecking order, with the strong ruling over the weak. They might also depict their culture as being focused on power acquisition. For example, in many fanfictions, young Frieza race members are trained from a young age to be powerful warriors.
First, give her unique abilities. Maybe she can control a different type of energy than other Frieza race members. Second, give her a complex personality. She could be arrogant like the typical Frieza race, but also have a hidden soft side. For example, she might secretly care about the well - being of a small group of beings on a planet she was supposed to destroy.