One idea could be that Harry's transformation into a monster girl makes him/her (depending on how the transformation affects gender identity) discover a whole new world of magical creatures that were previously hidden from normal wizards. He/She could form unique bonds with these creatures and use their newfound abilities to solve mysteries in the wizarding world.
Another plot could be that there is a prophecy about a monster girl saving the wizarding world. Harry, after turning into a monster girl, initially doubts that it could be him. But as he starts to embrace his new form and the powers that come with it, he discovers that he is the key to stopping an ancient evil that is about to rise again. He has to learn to control his new abilities quickly and gather allies from both the human and monster worlds.
One idea could be a quest where the main character has to rescue a monster girl who is being wrongly persecuted in the wizarding world. Maybe she has a unique power that the dark wizards want to use for evil, and the protagonist, inspired by Harry Potter's courage, sets out to protect her.
A plot could revolve around a monster girl gazer who accidentally gets a special power that allows him to understand the languages of all monster girls. This leads to him becoming a mediator between different monster girl tribes that are at war. He uses his newfound ability to broker peace and in the process, falls in love with a particular monster girl from one of the tribes.
One idea could be a story where a young adventurer stumbles upon the world of the Monster Girl Matango. He has to navigate through their society, learning about their unique customs and powers. Maybe he forms an unlikely friendship with a Matango girl who helps him understand their world better.
One idea could be a story where a young adventurer stumbles upon a hidden forest inhabited by monster girls and fairies. The adventurer has to learn to co - exist with them and discovers that the monster girls and fairies have their own complex society and unique powers. For example, a mermaid - like monster girl who can control water helps the adventurer cross a dangerous river in the forest.
Perhaps a story where a group of monster girls from different parts of the island come together to protect their home from an unknown threat. A human who has some special knowledge or ability gets involved and they all have to learn to work as a team. This could involve a lot of character development as they overcome their differences and prejudices.
One interesting plot could be how Harry, now as a girl, has to deal with the different social dynamics in Hogwarts. For example, she might face different expectations from teachers and peers. Maybe she forms new friendships with female characters in a way that Harry as a boy never did before.
One idea could be a monster girl trying to fit into a human school. She might face challenges like understanding human social norms and dealing with the occasional bully who is afraid of her differences. For example, a mermaid girl could struggle with walking on land in the school hallways and constantly getting stares. Another plot could involve a monster girl falling in love with a human boy, but their relationship is complicated by the fact that her family doesn't approve of humans. This could lead to a lot of drama and the two of them having to fight for their relationship. Or perhaps a group of monster girls start a club at school to promote understanding between humans and monster girls, and they face opposition from some conservative humans who don't want them there.
A great plot for an 'everyday monster girl farm fanfic' might be a competition among the monster girls on the farm. They compete in tasks like growing the biggest vegetables, taking care of the most energetic animals, or creating the most beautiful flower beds. The winner gets a special prize, like a day off or a new magical tool for the farm. Along the way, there are rivalries, friendships formed, and lots of fun and humorous moments as the monster girls try their best in their own unique ways.
One idea could be that Naruto discovers a hidden village full of monster girls. They are initially suspicious of him but as he shows his kind heart and powerful ninja skills, they start to fall for him. For example, a cat - like monster girl might be charmed by how he plays with the village cats.
One idea could be that a monster girl, who has the power of a fairy, discovers a magical lemon grove. The lemons there have special powers and she uses them to help her friends in the monster world. For example, the juice of the lemons can heal wounds or give temporary powers like flight.