A possible plot could involve a mermaid who is lost on land and Bonnie finds her. The mermaid is being chased by some villains who want to capture her for her magical powers. Bonnie decides to protect the mermaid and with the help of her Pokemon, they go on a journey to find a way to return the mermaid to the sea safely while evading the villains at every turn.
One idea could be that Bonnie discovers a hidden mermaid colony while on a Pokemon adventure near the sea. The mermaids initially mistake her Pokemon for threats but then realize they mean no harm. Bonnie then has to help the mermaids protect their home from a group of poachers who are after rare sea Pokemon that live near the mermaid colony.
Maybe Bonnie has a strange encounter where she is magically turned into a mermaid herself. She then has to learn how to swim and communicate with other mermaids using her new form. Along the way, she discovers that her Pokemon also have some unique abilities in the underwater world. For example, her Dedenne could use its electric powers to create beautiful light shows underwater.
One idea could be a Pokemon that has the ability to transform into a mermaid and it goes on a journey to find its true origin. It could face challenges like being hunted by humans who want to study its unique form.
Maybe there's a fanfiction where Ash and Bonnie enter a Pokemon tournament that's different from the usual ones. This tournament has strange rules, like Pokemon can only use moves that start with a certain letter. They have to quickly train their Pokemon to adapt and come up with new strategies. Along the way, they meet old friends and rivals who also want to win this unique tournament.
A possible plot idea is that there is a mermaid - themed Pokemon tournament. Misty enters it, thinking it's just a regular competition. But as she progresses, she realizes that the real purpose of the tournament is to find a human worthy of a special mermaid - related power. Misty has to compete against other trainers, all while uncovering the mystery behind the tournament and the power it offers.
In the fanfiction, Bonnie's Pokemon might develop new abilities or behaviors due to the mermaid influence. Her Sylveon could start to communicate with the mermaids in a unique way, perhaps using its ribbons to send messages. This would make Bonnie see her Pokemon in a new light, and their relationship would grow deeper as they all adapt to this new situation together.
One idea could be exploring Ariel's life after she becomes human. Maybe she has trouble adjusting to some of the more mundane aspects of human life, like cooking or doing laundry. Another could be a story where Ursula's sister comes to seek revenge, but Ariel has to convince her that not all humans are bad.
One idea could be exploring the relationship between Melody and a new mermaid friend from a different part of the ocean. They could go on adventures together and discover hidden treasures.
For Mermaid Melody fanfiction, you could have a plot where a group of mermaids form a band to compete in an underwater music competition. But there's a catch - one of the judges is a sea witch in disguise who wants to steal their voices if they win. Another plot could be about a mermaid who is born with the ability to see the future. She tries to use this power to prevent disasters in the underwater world, but some mermaids are superstitious and think she's a bad omen. Also, a story about a mermaid who swaps bodies with a human girl for a day could be really interesting. She has to navigate the human world while the human girl has to deal with the underwater world.
Another plot could be about the mermaid learning more about the human world in a different way. Instead of just falling in love with the prince, she discovers a hidden talent among humans like music or art and tries to bring it back to the underwater world. This could create a whole new set of adventures and challenges for her. For example, she might have to find a way to communicate with a human artist without revealing her true identity at first.
One idea could be exploring what would happen if Ariel had a secret power she didn't know about until after she became human. For example, she could have the ability to communicate with all sea creatures, not just the ones she already knew. This would create new challenges and relationships on land.
One idea could be that the baby has some sort of special power. Maybe it can communicate with the spirits like Bonnie, and this causes both joy and concern for Bonnie and Stefan. They have to protect the baby from those who might want to use its power for evil.