Well, start with the OC. Decide if the OC is male or female, young or old. In an H2O and mermaid setting, perhaps the OC has some special connection to water. Maybe they are a scientist studying marine life. For the love story, introduce conflict. For example, there could be an evil sea creature that wants to keep the mermaid away from the OC. The mermaid and the OC then have to fight against this obstacle. Also, don't forget about the magic aspect of mermaids. They could have special powers like healing with their tears or communicating with sea animals, which can add an interesting layer to the love story.
In these fanfictions, the theme of transformation is quite common. The OC might transform in some way, either in their personality or in their understanding of the world because of their encounter with the mermaid. Another theme is the power of friendship. Alongside the love story, the mermaid and the OC could form strong friendships with other characters in their respective worlds. And a theme of mystery also exists. The mermaid's world is full of secrets, and the OC is constantly trying to understand it, which adds an element of mystery to the overall story.
It depends on the specific H2O concepts. Some concepts are facts. For example, water (H2O) has a unique molecular structure that gives it its well - known properties like high heat capacity. This is a scientific fact. However, some might spread misinformation about H2O, like false claims regarding its ability to cure all diseases when consumed in large amounts, which is clearly fiction.
No, H2O itself is not a cause of acid rain. Acid rain is typically caused by the presence of pollutants like sulfur dioxide and nitrogen oxides in the atmosphere.
One common theme is friendship. Fans often explore how Will and Bella's friendship develops over time, especially considering Bella's mermaid secret. It's about their loyalty and how they support each other.
One common theme is the clash of different worlds. Since Percy comes from a world of demigods and H2O is about mermaids and a more aquatic - focused world, there's often a lot of adjustment and misunderstandings as the characters from both universes interact.
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.