Yes, there might be. The world of fanfiction is vast and diverse. With the popularity of both Harry Potter and the concept of Ryuji Jakkan (assuming it's a known or created concept), it's very likely that some fans have combined them in their creative works. However, it may not be as mainstream as some other Harry Potter fanfictions.
One common theme could be power and its consequences. Since Percy is an elder god, he has a great deal of power, and the fanfiction might explore how he uses or misuses it.
A common theme is friendship - turned - love. They start as friends and gradually develop deeper romantic feelings. Another theme is mutual support. They help each other through tough times, like Haru being there for Ryuji when he has family issues or Ryuji giving Haru confidence in social situations.
One common theme is friendship. Since Ryuji is part of the B Project, fanfics often focus on his friendships with the other members. Another theme could be his journey to achieve his dreams as an idol.
One common theme could be redemption. Given Kamoshida's actions in the game, fanfic might explore his path to redemption in relation to Ryuji. Another theme could be friendship or an unlikely bond forming between them.
I'm not sure specifically which 'Percy is one of the elder goda fanfiction' works are good. You could try searching on fanfiction platforms like Archive of Our Own. They usually have a wide range of works and user reviews to help you find interesting ones.
One popular akira x ryuji fanfic is 'The Bond Beyond the Screen'. It delves deep into their friendship and how it could potentially turn into something more. The character development in it is really well - done.
One of the common themes is self - discovery. In many 'akira kurusu x ryuji fanfic', both characters learn more about themselves while being in the relationship. Also, loyalty is often emphasized, showing how they are always there for each other no matter what. There are also some fanfics that touch on the theme of redemption, where they help each other overcome past mistakes.