One idea could be a cat girl who discovers she has special powers and has to use them to save her city from an evil villain. Another could be a cat girl falling in love with a human in a world where such relationships are frowned upon.
Well, you could have a story where a cat girl is part of a secret organization of magical beings. She has to prove herself among them while also dealing with her own insecurities about being different. Also, a cat girl who accidentally gets transported to a future world and has to adapt to the new technology and society.
One idea could be that the cat girl maid has special powers that she uses to protect her master from a mysterious threat in the mansion. For example, she can transform into a more powerful feline form at night.
One idea could be that Cat and Beck get lost in a magical forest during a theater production rehearsal. They encounter strange creatures that force them to rely on each other more than ever, strengthening their bond.
A possible plot is that the cat OC is a magical being from a different dimension. It gets lost in the Naruto universe and Naruto helps it. In return, the cat OC teaches Naruto some unique chakra - control techniques that it has from its own world, which gives Naruto an edge in battles.
One idea could be that Black Cat steals a valuable item, and Spiderman has to track her down. But when he finds her, they discover a bigger threat together and have to team up to stop it.
One idea could be a new student arrives at the Gallagher Academy with a mysterious past and special skills that the other girls don't have. This new character could bring in a new set of challenges and friendships. Another plot could be a mission that goes wrong and the girls have to use their wits and training to get out of a tricky situation. Maybe they get trapped in an enemy's lair and have to find a way to escape while also gathering intelligence.
A 'volleyball girl fanfic' could focus on a transfer student who is a volleyball prodigy. She has to adjust to a new school, new teammates, and new coaching styles. Along the way, she forms deep friendships and rivalries, all while trying to help the team win the championship.
One idea could be that as a girl, Ben has to face different social challenges while still using the Omnitrix to save the day. For example, some might underestimate her because of her gender, but she proves them wrong with her heroic deeds.
One idea could be a Lamia Girl who lives in a hidden forest and befriends a lost human adventurer. They help each other understand their different worlds.
A territorial dispute could be another plot. Black Cat has been operating in a certain part of the city for a while, and Catwoman moves in. They start a battle of wits and skills to see who gets to claim the area as their own hunting ground for valuable items. This could involve a series of rooftop chases and close - quarter combat scenes in the city's seedy alleyways.
One plot idea could be that Catwoman and Black Cat team up to steal a valuable artifact that has been causing chaos in the criminal underworld. They start off as rivals, each with their own motives, but as they work together, they begin to respect and even like each other.