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.
His hair could also be a plot device in a more comical way. Imagine a situation where his hair has a mind of its own and keeps getting him into embarrassing situations. Like it gets stuck in a door right before a big fight, and he has to struggle to free it while the villain is making fun of him.
First, understand the characters well. Saitama is bored with his power and just wants a good fight, while Boros is a proud and powerful alien seeking a worthy opponent. Then, come up with a unique plot. Don't just rehash their fight from the original. Maybe create a new world or situation for them. For example, a world where all heroes have lost their powers and Saitama and Boros have to work together to save the day. Also, good dialogue is key. Make it sound like how the characters would actually talk. Saitama's simple and straightforward speech and Boros' more grandiose way of speaking.
Genos would be an obvious choice as his student. Genos is always eager to learn from Saitama and improve his skills. Also, some of the lower - ranked heroes like Mumen Rider could be his students. Mumen Rider has a strong sense of justice but lacks in power, and Saitama could teach him some basic self - defense techniques.
One unique trait could be his hidden insecurities. Despite his overpowered strength, Saitama might secretly worry about being alone in his power level. He could feel like no one truly understands him. In fanfiction, this could lead to some interesting character development, like him trying to find a true equal or friend who can see past his strength.
One way is to introduce a personal conflict for Saitama. For example, he discovers that his extreme strength has unforeseen consequences for the world or for his relationships. This could lead him on a journey of self - discovery. He might have to make sacrifices or learn to control his power in a new way. This arc would show his growth as a character as he grapples with these new challenges.
Tornado of Terror would likely be one of the first to try and take on Evil Saitama. She's powerful and confident, but she would soon realize the extent of his power. Mumen Rider, despite being weak, would still stand up to Evil Saitama out of a sense of justice. He would be quickly defeated but his act of courage might inspire other heroes to step up.
Their relationship can be developed by having them face more personal challenges together. For instance, if Genos' family past is explored and Saitama helps him come to terms with it. Or they could have a fight over a difference in opinion, like how to handle a new, extremely powerful villain. After the fight, they realize how much they mean to each other and their bond grows stronger.
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.