One interesting fanfiction storyline could be that Genos discovers a prophecy that Saitama is going to lose his powers. Genos then goes on a mad quest to find a way to prevent this from happening. He visits all kinds of strange places and consults with various powerful beings. Another could be that there is a competition among heroes to see who can train the best new recruit, and Saitama and Genos enter together. They face off against other hero - trainer pairs in various challenges. Also, a story where Genos creates a virtual reality world for Saitama to experience different kinds of battles that he normally wouldn't encounter in the real world, just for Saitama's amusement.
One popular storyline could be them going on a training journey together. Genos, being the eager learner, and Saitama, with his overpowered strength, could teach Genos new techniques in unique ways. Another could be them facing a new, extremely powerful villain that challenges even Saitama, and Genos has to step up in unexpected ways to assist. A third one might be a story where they get transported to a different dimension and have to find their way back while dealing with the strange new world and its inhabitants.
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.
One common theme is the growth of their relationship. It could be Genos learning more from Saitama and becoming a stronger hero, not just in terms of power but also in terms of character. Another popular theme is the comical situations they get into. Since Saitama is so overpowered and Genos is very serious, their interactions often lead to humorous scenarios. Also, some fanfics explore the idea of them facing a threat that only their combined efforts can overcome, highlighting their unique bond.
Well, one way to portray their relationship differently is to make it a more competitive one. Genos could constantly be trying to outdo Saitama in small tasks or hero - related activities. On the other hand, it could be a relationship based on mutual admiration from afar. Genos looks up to Saitama but is too shy to get too close. And then there's the possibility of portraying it as a reluctant partnership, where they don't really like each other at first but are forced to work together and gradually grow on each other.
Writers develop their characters by exploring their backstories more deeply. For Genos, they might expand on his past traumas that led him to become a cyborg and his determination to avenge his family. For Saitama, they could dig into his days before becoming so powerful. Another way is through dialogue. The conversations between Genos and Saitama can show their growth and how they influence each other. For example, Genos might start to question his own motives after talking to Saitama about the true meaning of being a hero.
Genos is still kicking in the One Punch Man manga. The author has managed to keep him in the storyline without killing him off. There's always the possibility in the future, but for now, he's alive and fighting.
Genos would probably be even more in awe of Saitama. He already idolizes him, but with Saitama being S - Class, Genos might see him as even more untouchable. He could become more protective of Saitama's new status, trying to fend off any detractors or those who might try to take advantage of Saitama.