One possible plot could be that Gohan's wish brings back the Saiyans, but they return with their old warrior ways and have to adjust to the current state of Earth. There could be conflicts with Earth's inhabitants who are afraid of their power at first.
Maybe in the fanfiction, when Gohan wishes the Saiyans back, they come back without their memories. Gohan then has to help them regain their Saiyan identity while also protecting them from those who might want to take advantage of their powerlessness. This could lead to a lot of character - building moments and adventures as they rediscover their heritage.
Cell could also be a possible antagonist. Even though he was defeated, if the Saiyans are brought back, it could disrupt the balance that was achieved after his destruction. He might be revived or some remnant of him could emerge to oppose the Saiyans' return.
One possible plot could be Gohan going back in time to the Saiyan saga. He could use his knowledge of future events to prevent certain tragedies. For example, he might try to save the Saiyans from Frieza's wrath. He could also train with the younger versions of Goku and the other Z - fighters, sharing his advanced techniques and knowledge, which would significantly change the power dynamics in the battles against the Saiyans and later enemies.
It could lead to all kinds of interesting plot twists. Maybe they come back stronger or with new abilities.
Perhaps the biggest plot twist would be if Future Gohan's time - traveling somehow connects to a greater cosmic force or an ancient prophecy. His journey back in time could be part of a larger plan that he wasn't aware of. This could introduce new enemies or allies that are related to this cosmic plan. It might also mean that his actions in the past are not just about saving his own future, but about saving the entire universe from a much greater threat that was yet to be revealed.
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 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 this fanfiction, Gohan might change important events in the past. For example, he could prevent certain villains from getting stronger or save characters who died previously.
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.
Perhaps Hercule tries to train under Gohan in a really clumsy and disrespectful way. He doesn't follow Gohan's instructions and constantly brags about his own non - existent skills. This could lead to Gohan snapping at him out of frustration for his lack of discipline and respect.
Well, it could be about Naruto and Gohan getting transported to the Digimon world. Maybe they team up with some Digimon to fight a common enemy. They could use their unique abilities like Naruto's jutsu and Gohan's ki powers in combination with the Digimon's attacks.