There are many places to find such fanfiction. Firstly, Fanfiction.net has a large collection. Browse through the Naruto and Soul Eater sections and look for stories that specifically mention Patty. Another option is Archive of Our Own. It has a great tagging system which can help you narrow down the search to exactly what you're looking for. Some fanfiction might be about how Patty from Soul Eater could interact with the characters in Naruto, or it could be a more complex crossover story with an interesting plot.
One common theme is adventure. Since they are both in the world of Soul Eater which is full of battles and quests, fanfictions often involve them going on adventures together.
One great fanfiction is 'The Adventures of Kid, Liz and Patty'. It has a really interesting plot that shows their daily lives in the Soul Eater world, with some unique challenges they face together. The author does a wonderful job of portraying their relationships, especially how Kid's perfectionist nature interacts with Liz and Patty's more carefree attitudes.
One plot idea could be Patty somehow getting transported to the Naruto world and using her Soul Eater abilities to fight alongside the ninjas. For example, her weapon skills could be a great asset in battles against the Akatsuki.
Well, a major theme is cooperation. Since they are often in battles or dealing with the strange and dangerous in the Soul Eater world, they need to cooperate. Their different skills and personalities come together for this. Another theme could be discovery. They might discover new things about themselves, each other, or the world around them. And there's also the theme of protection. Liz and Patty protect Kid, and Kid also has a sense of protecting them, which is explored in many fanfics.
The popularity comes from the unique dynamic between the characters. Kid is so serious about symmetry and his role as a Shinigami, while Liz and Patty are more laid - back and fun - loving. When combined in fanfictions, it creates interesting scenarios. For example, in many fanfictions, Liz and Patty often get Kid out of his overly - serious mode, which is really entertaining.
One great fanfic could be 'The Adventures of Kid, Liz and Patty'. It often shows their unique bond and how they face various challenges together in the Soul Eater universe. Another one might be 'Kid's Guardians' which focuses on Liz and Patty's role in protecting Kid. There are also some fanfics that explore their friendship in a more comical way, like 'The Hilarious Trio' where they get into all sorts of zany situations.
You can try fanfiction websites like Archive of Our Own (AO3). There are usually a lot of works related to different pairings, including Kid x Patty. Just search for the relevant tags on the site.
One great Crona x Soul fanfiction is 'The Bond Beyond'. It delves into how Crona and Soul's relationship develops in a more in - depth way than in the original series. It shows them learning about each other's pasts and how they grow together. Another one could be 'A Different Kind of Friendship'. This fanfiction focuses on how they start as friends but there are hints of deeper feelings emerging as they face various challenges in the world of Soul Eater.