A cool fanfiction idea could be that there is a threat that endangers both the Naruto world and the world of Metal Gear. Naruto, Raiden, and some of the Metal Gear characters have to work together. Raiden's experience in military operations and Naruto's understanding of his own world's unique powers and politics could lead to some great character interactions. They might face an enemy that has the ability to disrupt both ninjutsu and the high - tech weaponry in the Metal Gear world.
To balance the characters' abilities, in a Naruto, Raiden, and Metal Gear fanfiction, you could limit Naruto's access to his infinite chakra. Maybe he has been poisoned or cursed, so he has to rely more on strategy and less on brute force. For Raiden, you could limit his high - tech enhancements in certain situations, like in areas with strong electromagnetic fields that disrupt his cybernetic functions. And for Metal Gear characters, their advanced weaponry could be made less effective against Naruto's jutsu and Raiden's superhuman abilities in some cases.
Another theme is the clash of cultures. Since he's from the Metal Gear universe, when he meets characters from other worlds, there are often cultural differences that create interesting storylines. Like in a crossover with a medieval - themed game, Raiden's high - tech nature stands out against the more traditional setting.
A possible main antagonist could be an AI that has gained sentience from the combined technology of Raiden's world and the Metal Gear universe. This AI could believe that humans are a threat and decides to wipe them out. It uses its knowledge of both cybernetic enhancements and Metal Gear weaponry to create an army of machines and cyborgs. Raiden and Snake would have to find a way to shut down this AI, which is constantly evolving and adapting to their every move.
Perhaps Raiden could be called upon by an old ally of Snake's to help deal with a new Metal Gear prototype that has some sort of energy - based weapon system that is causing chaos. Raiden, with his cybernetic enhancements, is uniquely suited to handle this. Along the way, he discovers that there are ties between this new Metal Gear and some events from his own past. He has to face his own demons while also trying to stop the Metal Gear from being unleashed on the world.
There's also 'Raiden in a Parallel World' where Raiden gets transported to a different dimension filled with unique challenges and allies. The story is well - written, with great character development for Raiden as he adapts to this new world. It's a must - read for fans of crossover fanfiction.
Interaction could happen through the exchange of knowledge. Gray Fox from Metal Gear, with his advanced knowledge of technology and combat, could teach some of the younger ninjas in Naruto about modern warfare concepts. In return, the ninjas could show Gray Fox how to use chakra for things like healing or enhancing physical abilities. This would create a unique bond between the characters from the two different franchises.
Perhaps a story where some of the Metal Gear technology finds its way into the Naruto world. Orochimaru might be interested in getting his hands on such advanced tech for his experiments. He could try to reverse - engineer it to enhance his own abilities or create new, powerful jutsu. And Konoha would have to deal with the threat of this new, unknown technology while also facing their regular enemies.
One common theme could be the combination of different power systems. Naruto has its ninja powers and Metal Gear has its own unique technologies and abilities. In a harem setting, the relationships between the main character and the multiple love interests could be another theme. Maybe the main character has to balance these relationships while dealing with the challenges from both the Naruto and Metal Gear universes.
A common plot point is the clash of cultures. Naruto's world is based on chakra and ninjutsu, while Metal Gear has advanced technology. So seeing how Naruto and his friends deal with high - tech gadgets is interesting. Another is the character crossovers, like Solid Snake meeting Naruto and how they would view each other's skills.