A crossover with Pokémon could also work well. The inklings and octolings could enter the Pokémon world and start trading Pokémon while also using their ink skills in Pokémon battles. For example, they could use their ink to create obstacles or distractions during a Pokémon battle, adding a new and interesting dynamic to the battles.
One idea could be that Naruto characters are transported into the Splatoon world. They might initially be confused by the ink-based battles and the unique species. For example, Naruto could mistake an Inkling for a strange ninja from another land and challenge them to a friendly spar, only to find out about the ink shooting mechanism. Another plot could involve the Akatsuki from Naruto trying to steal the valuable ink resources in the Splatoon world for their own purposes. They would face off against the Splatoon heroes who are determined to protect their world's resources.
One idea could be a story where Pokemon are able to use the ink - based abilities from Splatoon. For example, Pikachu could shoot out electric - charged ink to battle opponents. Another idea is a crossover world where trainers have to compete in both Pokemon battles and Splatoon - like ink battles. Maybe a Pokemon like Squirtle could be really good at the ink battles because of its natural water - shooting abilities.
One idea could be a human getting transported into the Splatoon world and having to learn the ways of inklings and octolings to survive. They could start by learning how to use the unique weapons in Splatoon and participate in turf wars.
The combination of different universes is the most interesting part. For example, when Splatoon 2 characters cross over with Pokémon, seeing the inklings and octolings interact with Pokémon and use their ink powers in the Pokémon world is really cool.
One interesting plot could be that Bowser teams up with the Octarians in the Splatoon world. He wants to use their ink technology to take over both the Mushroom Kingdom and the Splatoon world. Mario has to then form an alliance with the inklings. He travels through different ink - filled levels, learning new skills like swimming in ink and using ink - based weapons. Along the way, he discovers secrets about the connection between the two worlds. They finally face Bowser and the Octarian leader in a huge battle where Mario combines his classic moves with the ink - powered attacks of the inklings to save both worlds.
One interesting idea could be a crossover with "Moana". Elsa's ice powers and Moana's connection to the ocean could create a really cool dynamic. Maybe Elsa accidentally freezes part of Moana's ocean and they have to work together to fix it. Another could be with "Tangled". Rapunzel's long hair and her adventurous spirit combined with Elsa and Anna's journey in Frozen 2 would be exciting. Rapunzel could use her hair to help them climb mountains or cross chasms. A third idea is a crossover with "Beauty and the Beast". Belle's love for books and knowledge could help Elsa understand more about her powers and the history of magic in the Frozen world.
One idea could be that the Hypnoshades have a hidden power that only a select few inklings can unlock. And this discovery leads to a race among different teams to find out more about it.
There are fanfictions that focus on the backstories of the existing characters in Splatoon 2. For example, a story about how Agent 3 became such a skilled fighter. It could involve their early training days, the challenges they faced, and how they overcame them to become one of the top agents in the game.
A Rambo crossover fanfiction could involve him crossing over into the Star Wars universe. Rambo's guerilla warfare tactics could be interesting in a galaxy far, far away. Maybe he helps the Rebel Alliance in a ground - based battle against the Empire. Or a crossover with the Predator series. Rambo would be a worthy opponent for the Predator, and the fight between them in the jungle could be epic. Also, a Rambo and John Wick crossover would be intense, two highly skilled fighters on the same side or perhaps initially at odds.
One idea could be a crossover with a modern military setting. The Decepticons could be trying to steal advanced military technology. Another is a crossover with a post - apocalyptic world where they are competing with other factions for resources. A third could be a crossover with a magical realm, with the Decepticons trying to harness the magic for their own evil purposes.