Mumen Rider could be an interesting main character choice. His unwavering sense of justice and his determination despite being a relatively weak hero could be the focus. In a daily life fanfiction, we could see how he trains, his interactions with civilians, and how he looks up to heroes like Saitama even though he may not be on the same power level.
Well, perhaps a plot where Saitama tries to teach Genos some really mundane daily skills, like grocery shopping but in a super - hero - ish way. For example, he shows Genos how to find the best deals on discounted monster - fighting gear while also picking up some eggs and milk.
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.
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.
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.
Maybe a former villain who is reborn with a new moral compass. They could start using their villainous skills for good, which would make for an interesting main character as they navigate their new life in the world of One Punch Man, trying to make amends for their past deeds while also fighting new threats.
One way it could be imagined is if a new, extremely powerful villain emerged. This villain might have the ability to nullify Saitama's strength, perhaps by some sort of reality - warping power. In the fanfiction, Saitama could be caught off - guard by this new threat, and despite his best efforts, succumb to the villain's attacks. It would be a very dark turn for the One Punch Man universe.
Saitama might be really frustrated with Mosquito Girl. Since he can defeat most powerful foes with one punch, but a mosquito girl would be a different kind of annoyance. She could be constantly buzzing around and trying to bite him, and Saitama would probably just try to swat her away like a normal mosquito at first. But when he realizes she's a 'villain' in her own right, he might just give her one quick punch to end the nuisance.
One possible plot could be that Tornado initially challenges Saitama out of pride. She sees his nonchalant attitude and wants to prove that her psychic powers are superior. Saitama, being Saitama, just goes along with it. As the battle unfolds, Tornado throws everything she has at Saitama, but he just dodges casually. Eventually, Saitama throws a light punch that knocks Tornado back, but not seriously hurt, which makes her realize his true strength.
The other heroes in the Hero Association would be in shock. Saitama was like an unbeatable force among them. His death would make them realize how vulnerable they really are. They would have to reevaluate their own strength and the safety of the world. Some might be inspired to train harder, while others could be paralyzed by fear.
Saitama would win. Saitama's whole shtick is that he can defeat any opponent with one punch. All For One is powerful in the My Hero Academia universe, but Saitama's strength is on a completely different level. His power is so absurd that it's hard to imagine any character from My Hero Academia being able to withstand his punch.