The fanfiction about Fubuki and Tatsumaki in One Punch Man is alluring because it gives a chance to expand on their characters. Fubuki, with her ambition to be a great hero, can be explored further. Maybe in a fanfic, she overcomes her insecurities related to her sister Tatsumaki's much stronger powers.
Many One Punch Man fanfics with Fubuki and Tatsumaki focus on their interactions with other characters too. They could be paired with Saitama in some comical or action - packed situations. Like, Fubuki trying to recruit Saitama into her group while Tatsumaki is constantly skeptical of his abilities.
If Saitama became a monster in fanfiction, his physical appearance would surely change drastically. His bald head, which is now a symbol of his simplicity and power, might take on a more menacing look. His eyes could turn red, and his muscles might bulge in an even more grotesque way. This transformation could also affect his relationships. Genos, for example, would be in a difficult position. He idolizes Saitama as his master, but if Saitama becomes a monster, Genos might have to fight him to protect the city.
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.
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.
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.
Saitama's true strength was recognized by many in One Punch Superman. With the help of his neighbor and teacher, Dr. Orochi, people gradually understood his strength. Dr. Orochi had once told Saitama that he had powers beyond that of a human, and that he could strengthen himself through training. In addition, Saitama's teacher, Hungry Wolf, also called him the " strongest human." In addition, other characters such as Superman and Atom also acknowledged Saitama's strength.
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.
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.