One idea could be to combine the power - up mechanics of Dragon Ball Z with the strategic battles of Fire Emblem. For example, characters in the fanfic could gain new abilities similar to Super Saiyan transformations during intense battles in the Fire Emblem - like battlefields. They could use these new powers to turn the tide of the fight against the enemy forces, which could be a mix of both Dragon Ball Z villains and Fire Emblem antagonists.
A possible plot could involve a portal that connects the Dragon Ball Z universe and the Fire Emblem world. Some of the Dragon Ball Z characters accidentally end up in the Fire Emblem realm. There, they team up with the Fire Emblem heroes to fight a common enemy that threatens both universes. They would have to learn to work together, with the Dragon Ball Z characters teaching their powerful combat skills and the Fire Emblem characters sharing their strategic knowledge.
Vegeta could be paired with Ike. Both are strong - willed and prideful characters. They would initially clash due to their similar personalities, but as they face a powerful enemy together, they would come to respect each other. Vegeta's Saiyan power and Ike's swordsmanship would make for an interesting combination in battles. They could also have some great banter as they compare their respective power levels and combat philosophies.
The plot might involve a villain who has the ability to steal both ki and chakra. This forces Goku and Naruto to team up. Goku, with his Super Saiyan forms, provides brute strength, while Naruto, with his various jutsu like Rasengan and his Sage Mode, offers strategic combat skills. They would have to combine their powers in unique ways to defeat this new threat.
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.
One idea could be a crossover where Goku and Naruto meet. Maybe they start off as rivals, each thinking their own world's way of fighting is superior. But then they face a common enemy that forces them to combine their powers. For example, a powerful demon that can absorb chakra and ki. They would have to learn from each other's techniques to defeat it.
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.
Well, a cool plot might be that the Sage of Six Paths in Naruto has a connection to the Kais in Dragon Ball Z. This connection leads to a situation where Naruto and Goku have to work together to stop an ancient evil that threatens both universes. For example, the evil could be a powerful demon that feeds on both chakra and ki. They would have to combine their powers and the powers of their friends to stand a chance. Naruto could teach Goku some of his shadow clone jutsu, and Goku could show Naruto how to achieve Super Saiyan forms.
One idea could be Gohan crossing over into the Naruto universe. He could team up with Naruto and use his Saiyan powers to fight against the Akatsuki. Another plot could be Gohan in the Harry Potter world, using his ki to defend Hogwarts from Voldemort. Or perhaps Gohan in the DC universe, fighting alongside Superman against a common enemy.
One possible plot could be that Thanos somehow gets his hands on the Dragon Balls. He wishes for the power to snap away half of all life in the universe even more easily. The Z - fighters sense this great imbalance and travel to the Marvel universe to stop him. Goku, being the most powerful Z - fighter, tries to fight Thanos but quickly realizes his strength is different from what he's used to. Vegeta might have to team up with Iron Man to come up with a technological way to counter Thanos' Infinity Stones while Goku trains to reach a new level of Super Saiyan to take on Thanos directly.
One idea could be a new villain from an unknown dimension arriving in the Dragon Ball universe. This villain has a unique power that nullifies ki attacks, forcing the Z fighters to rely on their martial arts skills alone.
One idea could be exploring a dimension where the Saiyans never lost their planet and became a peaceful, advanced civilization. Another could be a dimension where the Z - fighters have to face off against versions of themselves that are corrupted by dark magic. Or perhaps a dimension where the Dragon Balls have different wishes and limitations.