Another way to expand his backstory is to look at his family. Maybe he had a family that was really poor and that influenced his desire for strength. He might have wanted to be strong enough to change their situation. In fanfiction, we could see flashbacks of his family life, his parents' expectations, and how that all played into his development as a person who eventually became Saitama, the One - Punch Man.
One way is to delve deeper into his training. Maybe add more details about the hardships he faced during his intense training regimen. For example, he could have had to overcome various natural disasters that occurred while he was training in isolation, like surviving a volcanic eruption near his training area.
His pre - hero days can be explored. We could see how he interacted with normal people before becoming a hero. Perhaps he had a job that was really dull, and that was part of the motivation for him to seek power. Fanfiction could show his daily struggles at that job and how it led him to start his training journey.
One way is to explore his life before he became a hero. Maybe he had a normal job and was constantly frustrated with the mundanity of it. This could have been the catalyst for his intense training.
The concept could be expanded by giving the punch different properties. For instance, it could have the ability to nullify an enemy's special powers instead of just knocking them out physically.
A plot where Saitama travels to different dimensions in the One Punch Man universe. He could encounter strange versions of himself or other heroes and villains, leading to humorous and action - packed situations.
Well, a lot of One Punch Man fanfictions about heroes seeing Saitama are really interesting. Some focus on their initial shock at his power. For example, Genos is always in awe of Saitama's strength in the original work, and in fanfictions, this can be explored even deeper, like how he tries to understand the source of that power.
The plot could involve Saitama teaching a group of new heroes how to face their fears. He would tell them about his own journey, starting as an ordinary guy who decided to become a hero just for fun. Saitama could teach them that no matter how strong the enemy is, one should not be afraid to take the first step. He might use his one - punch knockout strategy as a metaphor for facing difficulties head - on, even if it seems impossible at first.
Genos had a tragic past. His hometown was destroyed by a mysterious cyborg, which led him to seek power and become a hero to prevent such tragedies.
I also like the scenes where Saitama is just casually hanging out with the heroes, and they're trying to figure him out. He doesn't fit into their idea of what a hero should be, and the awkward yet hilarious interactions that follow are a great part of these fanfictions. For instance, he might be eating a meal with them, and they're all secretly observing him, wondering how someone so ordinary - looking can be so strong.
Identity exploration is also a theme. The sister might be struggling with being in Saitama's shadow or trying to find her own identity as a hero or just as an individual. She could be trying to make a name for herself without relying on her brother's fame.
One good fanfiction could be 'Saitama's Sister: The Hidden Power'. It explores the idea of Saitama having a sister with her own set of powers. In this story, she tries to keep up with her brother's reputation while also finding her own place in the hero world.
One fanfiction that's quite popular is 'The Female Saitama's Adventure'. It takes the concept of a female Saitama and puts her in different comical situations in the One Punch Man universe. Another interesting one is 'Female Saitama: A New Hero'. It focuses on how she might interact with the existing heroes and villains in a more character - driven way.