One common theme is friendship development. Writers often explore how hajime and shun's relationship grows over time, starting from an initial meeting and evolving into a deeper bond.
One place to find hajime x shun fanfiction could be Archive of Our Own (AO3). There are often many different works there that explore their relationship in various ways, from friendship - focused stories to more romantic interpretations.
One common theme is friendship development. Since they are from the Tsukiuta world, writers often explore how their relationship grows from just acquaintances to close friends or something more. Another theme could be their shared dreams and goals within the Tsukiuta universe.
Another option is to check out dedicated Japanese fanfic sites if you can navigate them. Some Japanese fans write really interesting stories about Shun and Hajime. But be aware that you may need some translation tools as most of them are likely to be in Japanese.
Definitely! The Hajime no Ippo manga has a compelling plot with lots of exciting boxing matches and emotional character arcs. The way it portrays the sport and the growth of the main character makes it really enjoyable.