Captain America would be a great main character. His leadership and moral compass would be important in a crossover. And for the H2O side, Cleo could be a main character. Her ability to freeze water could be useful when the Avengers are facing enemies in cold environments or need to create barriers. They could have a lot of character development together, with Cap teaching Cleo about strategy and Cleo showing Cap the magic of the mermaid world.
Thor could also be a main character. His connection to water through his control of lightning and storms could link well with the H2O mermaids. And Bella from H2O could be a main character too. Her power to create shapes with water could be used in creative ways with Thor's powers. For example, they could create a huge water - lightning construct to defeat a powerful enemy together.
Definitely Iron Man from the Avengers. His high - tech suit and intelligence could be really interesting when combined with the water - based powers of the H2O mermaids. And one of the mermaids, like Rikki, could be a main character too. She's feisty and her power to boil water could create some really cool interactions with Iron Man's technology, like powering up some of his systems in a unique way.
In this fanfiction, the mermaids from H2O could be discovered by the Avengers. Maybe the Avengers are on a mission near the beach where the mermaids live. The mermaids' unique abilities, like controlling water, could be mistaken for a new threat at first. But then they realize they can work together. The mermaids could use their water powers to help the Avengers during a big battle against a water - based villain like Namor. They form an unlikely alliance and learn from each other's worlds.
It could be about the characters from Harry Potter finding themselves in the world of H2O. Maybe Harry and his friends end up at the beach where the H2O mermaids are. They could learn about the mermaids' powers and secrets, and the mermaids could be fascinated by magic from the wizarding world.
One possible plot could be that the characters from H2O, who have the power to transform into mermaids in water, end up in the wizarding world of Harry Potter. They could be mistaken for some kind of new magical creature. The Hogwarts students might be both intrigued and a bit wary of them. Maybe they could help the students in a Triwizard Tournament task that involves water in some way.
Well, perhaps the H2O girls are being chased by some sea monsters that are normally under Percy's jurisdiction. Percy and his demigod friends come to their rescue. In the process, the H2O girls learn about the world of Greek mythology and demigods. They could then join forces to fight off other threats that come their way, like an evil sea god who wants to take over both their worlds.
Maybe a magical item gets lost that is crucial to both the H2O and Mako Mermaids' worlds. It could be a pearl that has the power to keep the balance of the ocean's magic. A young mermaid from H2O and a young mermaid from Mako accidentally cross paths while looking for it. At first, they are suspicious of each other. But as they search together, they start to understand each other's powers better. The H2O mermaid can freeze water to access hidden caves, while the Mako Mermaid can use her singing to call upon sea creatures to help. Eventually, they find the pearl and in the process, they create a friendship that bridges the gap between their two worlds.
Love and relationships are also popular themes. The h2o characters might fall in love with characters from the other crossover story. This could create interesting relationship dynamics and storylines, like a mermaid falling for a human from a different fictional world.
Once upon a time in the underwater world where the mermaids from H2O and Mako Mermaids co - existed. A group of mermaids from both series decided to have a friendly competition. The H2O mermaids showed off their unique ability to turn water into different shapes, while the Mako Mermaids demonstrated their incredible speed in the water. As they interacted, they learned new things from each other and became great friends, vowing to protect the ocean together against any threats.
Annabeth from Percy Jackson could be really interesting. She's smart and strategic. In a crossover, she could be the one to figure out how the H2O girls' powers work and how they can be used to everyone's advantage. Also, Cleo from H2O has her own charm. She comes from a different background and her insecurities combined with Annabeth's confidence would make for great character development.
Edward and Cleo would also be a fascinating pair. Edward's brooding and mysterious nature combined with Cleo's kind - hearted and sometimes naive mermaid self could lead to some really interesting interactions. Maybe Edward could be intrigued by Cleo's water - based powers and Cleo could be both scared and attracted to Edward's vampire side.
I think pairing Hermione with one of the H2O girls would be really interesting. Hermione is so studious and knowledgeable about magic, while the H2O girl has her own unique water - related powers. They could learn a lot from each other. For example, Hermione could try to figure out the scientific basis behind the H2O girl's powers, while the H2O girl could show Hermione some new ways to interact with water magically.