A great plot could be that an ancient evil threatens both Naruto's and Deku's worlds. The two are brought together by a mysterious force. At first, they struggle to understand each other's abilities and ways of life. But as they train together, they learn to complement each other. Naruto teaches Deku some of his ninja stealth and combat strategies, while Deku shows Naruto how to better control his strength in a more precise way like using One For All. Eventually, they form a powerful bond and are able to defeat the ancient evil.
One possible plot could be Naruto and Deku finding themselves in a strange new world together. They have to combine their unique skills, Naruto's ninjutsu and Deku's One For All power, to face the challenges of this world and find a way back home.
Well, perhaps the plot could revolve around a tournament. In this 'naruto luffy deku crossover fanfiction', they all enter a huge, multiverse - wide tournament. Naruto shows off his cool jutsu, Luffy surprises everyone with his stretching attacks, and Deku displays his newfound strength. Along the way, they have to team up against some really tough opponents who don't play fair, and they grow closer as friends.
One antagonist could be Orochimaru from Naruto's world. He could be interested in the power of Quirks in Deku's world and try to capture Deku to study his power. He would be a formidable foe as he is a master of ninjutsu and has a lot of devious plans.
One idea could be that Naruto and Kurama have a day - out in the Hidden Leaf Village. They visit all the places Naruto used to go as a kid, like Ichiraku Ramen, and Kurama makes funny comments about human food. Another could be that they team up to prank the other villagers in a harmless way, just for fun.
A possible plot is that Villain Deku has a plan to destroy a major hero institution, and Hero Deku has to stop him. But when they meet, Hero Deku realizes that Villain Deku was once like him, full of hope. This makes Hero Deku hesitant to fight at full force. Or perhaps Villain Deku has kidnapped someone close to Hero Deku, and during the rescue mission, Hero Deku tries to convince Villain Deku to change his ways. Also, they could be from alternate universes where the roles are reversed, and they are forced to interact and learn from each other.
One plot idea could be that Naruto and Sasuke have a secret code they developed as kids that no one else knows about. As they grow older and face challenges, this code becomes crucial in saving each other. For example, when Sasuke is on the verge of being taken over by the darkness completely, Naruto uses the code to reach out to the part of Sasuke that still remembers their childhood bond.
Maybe Itachi is on a secret mission outside of Konoha and he saves Naruto from a group of rogue ninjas. Naruto, being Naruto, is immediately drawn to Itachi's strength and kindness. They start to train together in secret. As they train, Naruto discovers Itachi's past and the burden he carries. This leads to Naruto vowing to help Itachi find a way to clear his name in Konoha and they become close friends in the process.
One plot idea could be that Naruto has to enter a dangerous, cursed forest to save his friends who were kidnapped by a powerful dark ninja. He uses his new, untested jutsu to fight off the forest's deadly creatures and the dark ninja's minions. Another could be Naruto traveling to a different dimension where his friends are held captive by an otherworldly being, and he has to figure out the rules of this new world to rescue them.
One idea could be that they are paired for a special project at school. During the project, they discover new sides of each other. Deku could be impressed by Momo's intelligence and strategic thinking, and Momo could be inspired by Deku's determination. This could lead to a growing friendship that might develop into something more over time.
In 'Deku Goes Berserk' fanfiction, a great plot point might be how the other characters react to Deku's new, wild side. For example, Bakugo could initially see it as a sign of weakness, but later realize it's a powerful force that needs to be harnessed. This could lead to a whole new dynamic between them. Another aspect could be how Deku's transformation affects his relationship with All Might. All Might might worry that he's losing control and try to help him in a different way than before.
The plot could start with Naruto getting into trouble for being too noisy in the village. Ibiki is assigned to keep an eye on him. At first, they don't get along. But when Naruto discovers Ibiki's love for a certain type of flower that grows on the outskirts of the village, he decides to bring some for him. This small gesture starts to break the ice between them, and they slowly become friends.