The fanfiction could start with Raditz's sudden abduction of Gohan. Once he has Gohan, Raditz could take him to a desolate planet. There, he begins to test Gohan's limits, pushing him to the brink of exhaustion. Gohan, being a strong - willed character, resists Raditz's attempts to break him. Meanwhile, Goku and the Z - fighters start a desperate search for Gohan, leading to an epic showdown between Goku and Raditz when they finally find the location.
In a 'Gohan kidnapped by Raditz' fanfiction, the plot could involve Raditz trying to turn Gohan against his family. He could expose Gohan to the cruel ways of the Saiyan race that Goku has somewhat distanced himself from. Raditz might show Gohan visions of the Saiyan's former glory and try to convince him that his human family is holding him back from achieving true power.
Piccolo might also be a savior. He has a soft spot for Gohan since they trained together. He could use his strategic mind and powerful attacks to outwit Raditz and rescue Gohan. Maybe he teams up with Goku for an even more epic rescue mission.
It could be that Gohan is kidnapped by a group who wants to study the Saiyan physiology. They might be scientists from a different planet or a secret organization on Earth. They take Gohan in order to run various tests on him, not realizing the danger they're in if Gohan manages to break free. And his friends and family then have to go on a mission to rescue him.
One plot idea could be that Gohan's friends, like Krillin and Bulma, team up to rescue him. They might use some of Bulma's inventions to track Raditz. Another idea is that Gohan manages to outwit Raditz during the kidnapping. Maybe he uses his hidden power to escape Raditz's clutches briefly and leaves a trail for his father Goku to follow.
It could be a new villain that has emerged, someone who is jealous of Gohan's power and wants to make it his own. This villain might be from a far - off planet and has heard of the Saiyan legend.
The plot could involve Naruto being trained by some Saiyan techniques due to his relation to Raditz. He could face enemies that are much stronger than the usual foes in the Naruto world. And perhaps he has to hide his Saiyan side from his friends in Konoha at first, fearing their reaction.
In a more complex plot, Raditz could be sent back in time and he meets a young Launch. They end up on an adventure together, facing various enemies and challenges. Along the way, they start to develop feelings for each other, which is complicated by Raditz's knowledge of the future and his original mission.
Goku would be a mix of angry and worried. His Saiyan blood would make him want to rush into battle with Raditz right away. But he also knows how dangerous Raditz is, so he might first try to gather some allies, like Piccolo. He'd be constantly thinking about Gohan and how to rescue him as quickly as possible.
One possible plot could be that Gohan and 18 meet in a rather unexpected situation, like at a martial arts tournament. They start to have conversations and find out they have more in common than they thought. Gohan's kind and intelligent nature attracts 18, and her strong and independent personality intrigues Gohan. As they spend more time together, they gradually fall in love and decide to get married, facing some challenges from their different backgrounds along the way.
In the 'Bardock Saves Raditz' fanfic, perhaps Bardock discovers a way to time - travel. He goes back to the moment when Raditz is about to die. Bardock could use his own power to shield Raditz from Goku's Kamehameha. Then, they team up and start exploring other planets, trying to find a new place for the Saiyans to thrive, away from Frieza's tyranny.
In this fanfiction, Gohan could be a new member of the Straw Hat Pirates. He would bring his unique skills like the Kamehameha wave. His strength would be a great asset during their adventures, especially when facing strong foes like the Yonko.