Erza from Fairy Tail is known for her different armors and combat styles. If she were to team up with King from Seven Deadly Sins, King could use his floating ability to give Erza an aerial advantage. She could then use her different armors to perform unique attacks from above. Also, the magical abilities of the Fairy Tail guild could be enhanced by the power of the Seven Deadly Sins. For instance, the sin of greed could be used to make Wendy's healing magic more effective by making her more eager to heal and thus unlocking more of her potential.
Lucy from Fairy Tail has her celestial spirit magic. She could summon spirits to assist characters from Seven Deadly Sins in battle. Maybe a spirit could enhance Ban's ability to steal life force, making him even more powerful in combat. And the characters from Seven Deadly Sins could teach the Fairy Tail mages some of their combat skills, like how to better use their physical strength in combination with magic.
Some characters could be directly linked. For example, a power - hungry character might represent greed. They constantly seek more magic power or rare items.
The 'Seven Deadly Sins' in Fairy Tail fanfiction often serve as a way to explore moral and ethical themes. For instance, pride might be a trait of a powerful wizard who looks down on others. This can lead to conflicts within the fanfic's plot. Fanfiction writers can use these sins to develop complex relationships between characters as well.
A really cool plot twist could be that the magic in Fairy Tail is somehow connected to the sins in Seven Deadly Sins. So, when a Fairy Tail mage uses too much of a certain type of magic, it starts to manifest as one of the seven deadly sins. This could create a whole new set of challenges for the characters as they have to not only fight external enemies but also control their own inner 'sins' that are now linked to their magic.
Meliodas' strength could translate into being able to mine faster. He could break through the toughest of Minecraft blocks like bedrock (in a fanfic - world where that's possible). His sword skills could be used to fend off mobs more effectively, like one - hit kills on most enemies.
The fem Naruto character's ability to manipulate chakra could blend well with Fairy Tail mages' magic. For example, if she teams up with Lucy, her chakra could enhance the power of Lucy's celestial spirits. Her speed and agility from being a ninja could also be an asset in battles against fast - moving enemies in the Fairy Tail world.
The worlds could also be combined through the discovery of ancient prophecies that involve both. There might be a prophecy that foretells the coming together of heroes from two different realms to save all of existence. This would draw the characters from Fairy Tail and the Seven Deadly Sins together. As they search for the meaning of the prophecy and how to fulfill it, they would gradually integrate their two worlds. For instance, they might find that certain locations in each world are linked, and by traveling between these linked places, they can fully explore and combine the two worlds.
Naruto would probably be very curious about them. He'd start by asking a lot of questions. He might befriend some of them quickly, like he did with many characters in his own world. For example, he could bond with Diane because of her kind heart, despite her being a giant.
Naruto's rasengan could be combined with the physical strength of some of the sins. For example, if he teams up with Escanor, the power of the rasengan could be enhanced by Escanor's strength during the day. His shadow clones could be used for various tactics, like distracting enemies while the sins set up their attacks.
One interesting crossover could be the magic from Fairy Tail interacting with the powers of the Seven Deadly Sins. For example, Natsu's fire magic might combine with Meliodas' full counter in a really cool way during a battle against a common enemy. It could create a whole new kind of attack that is both powerful and visually stunning.
Obviously, Natsu would be one of the main characters. And from the Seven Deadly Sins, Meliodas is very likely to be a main character as well since he's the leader.