A possible plot could involve a mystery that the characters from both series need to solve together. The Loud House kids' knowledge of their town and the Recover Girls' special abilities would combine to uncover a hidden secret in their shared universe. For instance, there could be strange disappearances in Royal Woods that the Recover Girls' powers of recovery and the Louds' determination can help figure out.
Another plot could involve a love triangle among the Loud siblings' friends. They all end up at the Loud House often, and the love triangle causes some tension. But through various events at the house, like parties or family outings, they start to understand each other better and resolve their differences in a really sweet way.
One idea could be a time - travel plot where a character from the Loud House goes back in time and has to deal with changes in the family's history. Another could be a 'what if' scenario, like what if Lincoln had a different set of sisters. Maybe he could have all older sisters and the story could explore how that dynamic changes things.
Another way is through a mutual friend. Let's say there is a character who knows both the Loud House family and the Recover Girls. This character could introduce them, and then they start working on a community project together. For example, rebuilding an old community center. The Recover Girls could use their powers to heal the building's structural damage, while the Louds contribute with their creativity and manpower.
Maybe Linkin is from a different dimension and he accidentally lands in the Loud House world. He and Lily form a unique bond as he tries to find his way back home. They go on adventures together in the neighborhood, with Lily showing Linkin all the local quirks and Linkin teaching her some of his world's secrets.
One idea could be a story where the boy and the three girls form a study group. They start off not getting along well because of their different study habits. But as time passes, they learn from each other and become really good friends. They end up acing their exams together and have a big celebration at the end.
One idea could be that Lincoln Loud discovers a rare and powerful Pokemon in Royal Woods. He then has to keep it a secret from his sisters while training it. Another could be the Loud sisters each getting a Pokemon that reflects their personalities. For example, Lola might get a Jigglypuff because it's cute and girly.
A cool plot for 'the loud house crossover fanfiction' might involve a crossover with 'My Little Pony'. The ponies could come to Royal Woods, and the Loud sisters could be fascinated by their magic and cuteness. Lincoln might have to figure out how to get the ponies back to Equestria while also dealing with his sisters' excitement. Or perhaps the Loud family travels to Equestria and has to adapt to a world ruled by ponies.
One idea could be that Naruto somehow ends up in the Loud House world. Maybe he's on a mission and a strange jutsu goes wrong, transporting him there. He could use his ninja skills to help the Loud siblings out with their daily problems, like getting rid of a bully at school using his shadow clone jutsu.
One idea could be that the Loud family members gain superpowers similar to the Avengers and have to team up to save Royal Woods from an alien invasion. For example, Lincoln could be like Captain America, leading the group with his strategic mind.
A third plot idea is that a group of vampire hunters come to Royal Woods believing there is a vampire in the Loud House. Lucy has to use her wits and any vampire friends she might have made to outsmart the hunters and protect her family. This could involve some really exciting chase scenes and moments of clever deception.