The characters would interact in many interesting ways. Natsu, being hot - headed, might challenge Link to a fight at first. But then they could realize they are on the same side against a common enemy. Lucy would probably be fascinated by the magic and technology in the Zelda world and try to learn more about it. Zelda, on the other hand, could be intrigued by the Fairy Tail mages' powers and their guild system. She might see it as a way to better protect her own world.
One interesting plot twist could be that characters from Fairy Tail end up in the world of Legend of Zelda and they discover that their magic has a completely different effect. For example, Natsu's fire magic might interact with the magical elements in Zelda's world in a way that either helps or hinders their quest. Another could be that the Triforce has an unexpected reaction to the Fairy Tail mages' presence, perhaps granting them new powers or cursing them. A third plot twist might be that a major villain from Legend of Zelda teams up with a dark guild from Fairy Tail to take over both worlds.
A common theme is the combination of magic. Since both universes have their own forms of magic, fanfictions often explore how the magic from Zelda and Fairy Tail can interact or be combined. For example, the Triforce's power might be used in a Fairy Tail - style magic battle.
Another interesting plot could be the Legend of Zelda characters getting lost in the Fairy Tail world. They have to adapt to the new environment, make new friends, and figure out how to get back home. Along the way, they discover new things about themselves and their own powers. It's like a fish - out - of - water story but with the added bonus of magical elements from both universes. This type of plot can be used to introduce Zelda fans to the world of Fairy Tail and vice versa in a really engaging way.
Well, I know that Archive of Our Own (AO3) also has a decent collection. In these fanfictions, you might see crossovers where the magic system of Fairy Tail is incorporated into the Legend of Zelda universe. Writers often get creative with how the different powers and characters interact. For example, Link might have to team up with Natsu to defeat a common enemy.
One great 'Legend of Zelda Fairy Tail' fanfiction is 'The Link in Fairy Tail' which combines the unique elements of both worlds really well. The author does a great job of integrating Link's skills into the Fairy Tail guild's adventures.
Maybe Zelda herself could be transported to the Avengers universe. With her wisdom and magic, she could assist the Avengers in different ways. She could use her magic to heal the wounded Avengers or help Tony Stark understand some ancient technology that has similarities to her own world's tech. She could also provide strategic advice based on her experience dealing with Ganon in her own realm.
One idea could be that Link, from Legend of Zelda, somehow gets transported to the Naruto universe. He might initially be mistaken for a strange shinobi with his unique green tunic and hat. Link could use his combat skills, like swordsmanship and shield defense, to team up with Naruto and his friends against common enemies, such as the Akatsuki who are after powerful artifacts. Maybe the Ocarina of Time has some sort of power that the Akatsuki wants, and Link has to protect it while in this new world.
One more theme is the exploration of different moralities. The relatively simple good - vs - evil in Hyrule is contrasted with the more complex moral landscape of the DC Universe. This can lead to some interesting internal struggles for the characters as they navigate these different moral frameworks and try to figure out who the real enemies are and who can be trusted.
Some great Legend of Zelda crossover fanfiction concepts include a crossover with the Sonic the Hedgehog series. Link could be racing through the Green Hills Zone on Epona. A crossover with the Super Mario Bros. universe is also a fun idea. Link and Mario could join forces to rescue Princess Zelda and Princess Peach from the clutches of their respective villains. Additionally, a crossover with the Kingdom Hearts series would be epic. Link could interact with Sora and the other Keyblade wielders, exploring different Disney and Zelda worlds together.