Yes, there are quite a few. You can find them on various fanfiction websites. Some might focus on his growth as a player from a female character's perspective, showing how she witnesses his development in the sport.
You can try fanfiction.net. It has a large collection of fanfictions, and you might be able to find some great ones about Sawamura Eijun from a female - centered perspective there.
The theme of rivalry also exists in some fanfictions. While they are friends and teammates, there can be a friendly rivalry between them. This rivalry can be in terms of who is a better pitcher or catcher, or who can contribute more to the team. It adds an interesting dynamic to the stories and shows different aspects of their relationship.
Well, 'Harmony on the Field' is a miyuki kazuya x sawamura eijun fanfiction that's quite popular. It focuses on how their different personalities complement each other on and off the baseball field. It shows miyuki's strategic mind and sawamura's fiery spirit working together in a really engaging way. There are also some really nice character - development arcs in this fanfiction.
Since I don't have in - depth knowledge about Sawamura Harutarou's light novels specifically, it's difficult to point out the popular ones. But light novels often have distinct art styles for their covers, which might attract readers initially. His works could have themes like love and loss, where characters grow and change as a result of their experiences. There might also be elements of mystery, where readers are kept on their toes, trying to figure out what will happen next in the story.
Another interesting plot could be a time - travel fanfiction. Miyuki and Sawamura are sent back in time to the early days of their baseball careers. They use their present - day knowledge and skills to change some of the mistakes they made in the past, which in turn has a big impact on their current team's success.
Since I don't know much about Sawamura Harutarou's light novels, a possible starting point could be to look for any of his works that have been translated into your preferred language if you're not reading in the original Japanese. You can also try to find reviews or discussions on light novel forums or communities. They might be able to give you some insights into which of his works are more accessible or interesting for new readers. Another option is to start with the ones that seem to have the simplest synopsis, so you can ease into his writing style.
For Sawamura, his character could be developed by exploring his insecurities more deeply. In fanfiction, he could have moments where he doubts his abilities as a pitcher, not just in terms of his skills but also his mental strength. Miyuki could then be the one to help him through those tough times, which would strengthen their bond.
The ending of Girlfriend Girlfriend manga is quite complex and bittersweet. The characters go through various challenges and their relationships evolve in unexpected ways.