One idea could be to create an OC who is a half - human, half - monster girl trying to find her place in a world that fears her kind. She could go on a journey to prove that she's not a threat.
One idea could be a crossover with a popular fantasy RPG. The protagonist from Monster Girl Quest could find themselves in a world filled with different races and magic systems from the other game. They'd have to adapt and maybe form alliances with new characters. For example, if it was a crossover with 'The Elder Scrolls', the monster girls could interact with the various guilds in Skyrim, like the Thieves Guild or the College of Winterhold.
You could write a fanfiction about a monster girl oc who is an outcast in her own kind's society. Maybe she has a unique power or appearance that makes the others shun her. A human befriends her and together they embark on a journey to prove that she is not a danger but rather an asset to both the monster girl world and the human world. This would involve a lot of character development and exploration of themes like acceptance and prejudice.
One idea could be a quest where the main character has to rescue a monster girl who has unique magical abilities that are crucial to the wizarding world. Maybe she can communicate with magical creatures in a way no one else can, and dark forces want to use her for evil. So the protagonist teams up with his Hogwarts friends to find and protect her.
One idea could be that Ben Tennyson finds himself in a parallel dimension where the Omnitrix has transformed all the female characters into monster girls. He has to figure out how to change them back while also dealing with the new powers and personalities of these monster girls. Another plot could involve a group of evil forces trying to use the monster girl situation to take over the world, and Ben has to team up with some of the friendly monster girls to stop them.
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.
Another idea is an OC who is a transfer student from a very different monster culture. Maybe they come from a far - off land where monsters have different ways of scaring or being funny. This OC could bring in new techniques and ideas, causing a stir among the students and professors. They might struggle with the local monster language at first but then use their own unique language and cultural quirks to their advantage in a big project or competition. For instance, in a scare - off competition, they use a unique call from their home culture that confuses the opponents and gives them an edge.
Another plot could revolve around an OC who is a scientist. He discovers a new type of monster girl that no one has seen before. This discovery causes a stir in the Monster Musume community. As he tries to study and understand this new creature, he forms a special bond with her, and they face challenges together, like dealing with those who want to use the new discovery for their own gain.
One idea could be an OC who is a new student at Monster High and has a unique ability that no one else has, like the power to communicate with long - forgotten spirits. This could lead to all sorts of adventures as she tries to fit in while also dealing with the mystery of these spirits.
Another great storyline could involve a slime girl in the Monster Girl Quest fanfic. Maybe she discovers a unique power within herself that allows her to transform into different forms, and she uses this power to help the other monster girls and humans co - exist peacefully. For example, she could transform into a bridge to help humans cross a dangerous ravine in the monster - dominated land.
One idea could be that the mummy monster girl is an ancient protector of a hidden tomb. A young archaeologist stumbles upon the tomb and accidentally awakens her. She initially sees him as a threat but then realizes he has a pure heart. They form an unlikely alliance to protect the tomb from those who would loot it for evil purposes.