For a 'naruto destiny crossover fanfiction', a cool concept would be to cross it with the Star Wars universe. The shinobi could be like the Jedi or Sith, with chakra being a form of the Force. They might travel across different planets in the Star Wars galaxy, engaging in battles with lightsabers (modified to suit their ninja styles) and using their unique jutsus. Also, a crossover with the Avatar: The Last Airbender world could be interesting. Naruto characters could interact with the benders, learn about different bending techniques, and combine them with their own ninjutsu.
One idea could be to cross Naruto with another popular anime like One Piece. Naruto characters could end up on the Grand Line, facing pirates and searching for the One Piece while using their ninja skills. Another idea is to cross it with a fantasy series like Harry Potter. Picture Naruto and his friends attending Hogwarts and learning magic alongside their ninja training. Or perhaps a crossover with the DC Universe, where Naruto characters gain superpowers similar to the DC heroes and fight against villains in a new, urban setting.
Maybe in this crossover, Naruto has a vision of the Traveler from Destiny. Curious, he somehow manages to cross over to the Destiny universe. There, he meets the different classes of Guardians. He could learn about their weaponry and powers and in turn, teach them about chakra. They could then work together to stop a Vex invasion that is spreading across both universes.
A Destiny 2 and Mass Effect crossover fanfic would be cool. The Guardians could interact with the various alien species in the Mass Effect universe. They could exchange knowledge about their different forms of space travel and combat tactics. For example, the Guardians could show the Mass Effect characters how to use their Light abilities in battle.
One idea could be to have the Guardians from Destiny encounter the Normandy crew in Mass Effect. They could team up to fight a common enemy like a new, powerful alien race that has the technology to disrupt both the Traveler's Light in Destiny and the Mass Relay network in Mass Effect.
One idea could be to have the characters from Harry Potter interact with the Guardians from Destiny in a battle against a common dark magic - influenced enemy. For example, Harry Potter could team up with Cayde - 6 to fight off a horde of Death Eaters and Fallen that have somehow merged their powers.
One idea could be that the characters from RWBY are transported into the Destiny universe and have to learn to use the unique weapons and powers there. For example, Ruby could be fascinated by the Exotic weapons in Destiny and try to incorporate their technology into her Crescent Rose. Another plot could involve the Guardians from Destiny being sent to the RWBY world to help fight against the Grimm. They would have to adapt to the new environment and team up with the RWBY characters. The third idea is that a powerful enemy from the Destiny universe somehow crosses over to RWBY's world and the combined forces of both universes have to stop it.
One idea could be having the Guardians from Destiny team up with the Jedi in Star Wars. The Guardians' unique abilities with their Light powers could interact in interesting ways with the Force used by the Jedi. Maybe they could face a common enemy that threatens both their universes, like a powerful Sith who has somehow gained access to the Darkness from Destiny.
A third idea could be a crossover where some of the Destiny characters end up in the Naruto universe. They would have to learn how to use chakra and ninjutsu. The Guardians could be amazed by the different fighting styles in Naruto's world. And they could also share their knowledge of advanced weaponry and space - time manipulation with the ninjas, leading to some really unique battles and alliances.
Perhaps the Voldemort threat in the Harry Potter world is somehow connected to a Darkness - like entity in Destiny. Harry and his friends must learn new combat techniques from the Guardians or other Destiny characters to combat this new, more powerful form of the Dark Lord. They could also exchange magical and technological knowledge, which would be really cool to see.
One idea could be a group of Guardians from Destiny being transported to the Star Wars universe. They could team up with the Jedi to fight against the Sith and the Darkness that threatens both universes. Maybe they would introduce their advanced weaponry and abilities to the Star Wars characters.
Another plot could involve a shared enemy that exists in both universes. The combined forces of Mass Effect races and Destiny Guardians have to figure out how to defeat this enemy. They would need to overcome their differences in culture and combat styles to be successful.