Yes, there are quite a few. Some focus on an alternate universe where they have to team up for some strange reason. For example, in one fanfic, they have to face a new common enemy that is even more powerful than Muzan. Tanjiro has to put aside his hatred for a while to deal with this new threat.
A common theme is the power of their combined strength. Tanjiro has his own set of skills and Mitsuri has hers. Fanfics often explore how they use their combined powers to defeat powerful demons. Additionally, the theme of hope is often present. Their relationship gives them hope in the dark world of demon slaying, and they inspire others around them with their positive attitude and connection.
One great 'tanjiro x mitsuri fanfic' is 'A Bond Beyond the Demon Slayer Corps'. It really delves into their relationship, showing how their different personalities complement each other. Tanjiro's kind - hearted nature and Mitsuri's energetic and affectionate side create a really interesting dynamic in the story.
Definitely not. Genya remains outside the ranks of Hashira throughout the manga. This is because of a combination of factors such as his skills, experiences, and the overall direction of the story.
Well, the circumstances of Genya's death in the manga are quite complex. It involves a series of events and confrontations with powerful enemies. But I can't recall all the details at the moment.
You can try some well - known fanfic websites like Archive of Our Own (AO3). It has a large collection of fanfics from various fandoms, and you can easily search for tanjiro x muzan fanfic there. Just use the search bar and type in the relevant tags.