Some popular ones might be those that explore her relationship with other characters from the Marvel universe. For example, fanfics that focus on her friendship or team - ups with Natasha Romanoff. These often delve into their shared past and how they interact in different scenarios.
In many Yelena Belova x Reader fanfictions, the theme of redemption can be found. Maybe Yelena has a dark past and the reader helps her come to terms with it and become a better person. Also, the theme of discovery is quite popular. The reader discovers Yelena's true self beneath her tough exterior, and they form a deep connection. There are also stories that revolve around the theme of family, where the reader and Yelena create their own little family unit in a way.
Some dedicated Marvel fan forums might also be a good source. Fans often share their own fanfics or recommend ones they've read. You can join these forums and ask for recommendations. Just make sure to follow the forum rules while you're searching.
A common theme is the exploration of their relationship dynamic. Given their different backgrounds - Yelena from the Red Room and Kate as a self - made archer - hero, there's often a contrast and then a coming - together. Another theme is friendship evolving into love. They start as comrades or even reluctant allies and then develop deeper feelings.
One great place to find Yelena Belova x Reader fanfiction is Archive of Our Own (AO3). There are numerous stories there with different themes and plotlines. Some might focus on adventure scenarios where the reader and Yelena go on a dangerous mission together. Another option could be Fanfiction.net, though the quantity might be a bit less compared to AO3.
You can also check out Tumblr. There are often fanfiction snippets and links shared by fans. Some of the fanfictions might focus on their different personalities - Yelena's more brash and Kate's determination - and how they complement each other. They could be in a modern - day setting where they meet in a coffee shop and start off on the wrong foot but then slowly fall in love.