Well, perhaps the seven deadly weapons are actually keys to unlock hidden jutsu. In the fanfiction, Naruto might accidentally stumble upon one of these weapons and as he tries to figure out what it is, he discovers that it has a connection to a powerful and long - forgotten jutsu. Or, the weapons could be the creation of an old and evil ninja who planned to use them to conquer the ninja world, and now Naruto and his friends have to stop the resurgence of these weapons.
One idea could be the seven deadly weapons being tied to ancient ninja clans in the Naruto world. For example, a weapon might be hidden within a clan's secret temple and its discovery could start a race among different ninja groups. Another could be that the weapons are cursed and whoever wields them starts to be influenced by the deadly sin associated with each weapon, like the sword of wrath causing the wielder to have uncontrollable anger.
Another plot could involve fem Naruto being accused of the sin of envy. In the Seven Deadly Sins' setting, she could envy the powers or status of certain characters. She might see how powerful Meliodas is, for instance, and envy his leadership and strength, which could lead to her making some unwise decisions in an attempt to prove herself equal or better.
Another possibility is a story in which the power system of the Seven Deadly Sins is introduced into the Naruto world. Naruto and his friends could gain new abilities based on the virtues that oppose the seven sins. For instance, Sasuke might learn a power related to humility (opposing pride) which helps him in his journey of redemption. This would not only mix the two universes but also offer new character development arcs for the Naruto characters.
Orochimaru would be a great antagonist. He's always after power and the seven deadly weapons could be something he desires to add to his collection. He might use his dark jutsu to try and control the weapons for his own evil purposes.
One idea could be an OC who is a hybrid of two of the deadly sins, like pride and envy. This OC could struggle with the internal conflict of these two powerful emotions. For example, being envious of the power of other characters while also being too proud to admit it or ask for help. Another plot could be an OC who is on a quest to redeem the Seven Deadly Sins themselves, believing that they can be reformed. This would involve the OC facing many challenges and having to understand the true nature of each sin.
One idea could be a crossover where Naruto's world is invaded by the forces of the Seven Deadly Sins and Merlin from that universe has to team up with Naruto to stop them. Naruto's powerful jutsu and Merlin's magic could create some really interesting battle scenes.
One possible plot could be that Naruto, with his never - give - up attitude, teams up with Meliodas from 'The Seven Deadly Sins'. They could be on a quest to stop a new, powerful enemy that combines the dark magic from the world of 'The Seven Deadly Sins' and the powerful jutsu from the Naruto universe. Naruto's ability to make friends and his strong will could influence the members of the Seven Deadly Sins in positive ways, while their combat skills and unique powers could help Naruto in battles he might not be able to win alone.
A plot could be that Escanor and Merlin are tasked with training a new generation of knights. They have different teaching styles, with Escanor focusing on physical and mental fortitude, and Merlin on magical abilities. This leads to some humorous and also some tense moments as they try to work together.
A plot could involve Kirito being cursed by a powerful enemy related to the Seven Deadly Sins' lore. The curse affects his ability to log out or communicate with his own world. In order to break the curse, he has to help the Seven Deadly Sins complete a series of dangerous quests. Along the way, he forms deep bonds with each of the sins and learns about their pasts and how they are dealing with their own 'sins'.
One interesting plot idea could be that in the Minecraft world, the characters from Seven Deadly Sins are transported there. For example, Meliodas could be on a quest to find a special diamond that has the power to restore his lost strength. And the Minecraft mobs could be influenced by the sins. The zombies could be more aggressive due to wrath, and the pigs could be gluttonous and overeat the crops in the game.
Maybe a plot where Merlin discovers a prophecy that only Escanor can fulfill, but it requires him to sacrifice something dear to him. They embark on a journey to find a way around the sacrifice while also falling in love along the way. There could be many challenges like facing ancient guardians and deciphering cryptic riddles.