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.
Create backstories that involve lemons. For instance, a character was born near a lemon tree that was blessed by a powerful fairy. This made her have special powers related to lemons. She could be a monster girl with fairy powers who uses lemons to make potions to help other monster girls. Her appearance could also be influenced by the lemon tree, like having lemon - colored hair or eyes.
One common theme could be adventure. Combining the world of Naruto with monster girls and fairies often leads to exciting new adventures. Another might be friendship, as characters from different 'species' or groups come together and form bonds.
Well, often the fairy princess is a popular character. She usually has magical powers like the ability to heal or control nature. Another popular one could be the cat - girl monster. She has a cute and mischievous personality, which makes her appealing. And then there's the powerful dragon - girl monster who has great strength and can breathe fire, adding an element of danger and excitement to the story.
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.
I'm not sure of specific 'naruto monster girl fairy fanfic' stories off the top of my head. But you can try searching on fanfiction websites like Archive of Our Own. They usually have a wide range of fan - created stories in various genres related to Naruto.
The lamia is often quite popular. Her snake - like lower body gives her a unique and alluring appearance. She can be portrayed as mysterious and intelligent, which makes for an interesting character in fanfics.
In a 'Girl vs Monster' fanfic, the girl could be from a long line of monster hunters. She is the only one left in her family though. The monster she's up against is the one that killed her family. This adds an emotional depth to the story as she not only fights for survival but also for revenge. She might use her family's secret techniques to take on the monster.
It's hard to say it's a widely popular genre. 'Monster Musume' itself has a dedicated fanbase. But when it comes to 'harem' and 'lemon' elements in fanfic, these can be polarizing. Some people might be attracted to the idea of a harem in the Monster Musume setting, but the 'lemon' part can be off - putting to many. So overall, it may not be as popular as more general Monster Musume fanfic.
Well, you could have a fox - girl. Given Naruto's connection with the nine - tailed fox, it would be interesting to have a fox - girl in the harem. Maybe she has some of the same powers as the nine - tailed fox but in a more feminine and alluring way.