The fanfiction might focus on the world - building aspect. Since both Mighty Nein and Vox Machina exist in the same universe in the Critical Role world. The meeting could expand on the existing lore. Maybe they discover new places or secrets together. For instance, they could stumble upon an ancient ruin that neither group knew about before. This could introduce new magical items or threats that they have to face. It could also show how the two groups' different relationships with various factions in the world play out when they are together.
A possible plotline could be a joint quest to defeat a powerful and ancient evil that neither group could handle alone. This would force them to pool their resources and skills.
Percy from Vox Machina is often quite popular. His complex backstory, his skills with guns and his noble yet flawed personality make him stand out. In the fanfiction, his interactions with the members of The Mighty Nein can be really engaging, especially when it comes to discussions about technology and magic.
One idea could be a joint quest where the Mighty Nein and Vox Machina have to team up to defeat a powerful, ancient evil that threatens both their worlds. Maybe it starts with some strange magical disturbances that draw the attention of both groups.
Another plot point could revolve around a common enemy. A powerful villain might emerge that neither group can defeat alone. So, they are forced to team up. This would require them to put aside their differences and work together. There could be moments of tension as they struggle to coordinate their strategies, but in the end, they learn from each other and become stronger as a combined force.
Grog from Vox Machina and Fjord from the Mighty Nein. Grog is this big, brawny warrior and Fjord is a half - orc who is more reserved and still exploring his powers. Grog could be a bit of a mentor figure to Fjord in terms of physical combat, while Fjord could teach Grog some things about strategy and using his strength in a more calculated way.
One great place to start looking for Vox Machina Percy and Vex fanfiction is Archive of Our Own (AO3). It has a large collection with various themes and writing styles. You can also try Fanfiction.net, though the tagging system might not be as detailed as AO3's. Another option is to check out Tumblr. There are often fanfic recs and some writers might post their works directly there.
It's all about the characters really. Percy and Vex have such distinct personalities. In the original Vox Machina story, their interactions are full of tension and chemistry. Fanfiction writers love to expand on that. They can put the characters in different situations, like a magical adventure where Percy has to save Vex or a situation where they have to pretend to be a couple. All these possibilities make the fanfiction very popular.
One great story could be about their adventures outside of the main plot. For example, a fanfiction where Percy and Vex go on a solo mission to find a rare magical artifact. In this story, they might face challenges that test their relationship and individual skills.
Another place to check is FanFiction.net. There are many users who post their own takes on different characters and relationships, and you might find some interesting Percy and Vex fanfictions there. However, the quality can vary, so you might need to do some sifting through.