One different portrayal could be that Genos is the one who has to constantly save Saitama from his own carelessness. Maybe Saitama gets into all sorts of comical mishaps and Genos is there to bail him out. Another way is to have a relationship where they are complete opposites in terms of their emotions. Saitama is always calm and Genos is super emotional, and they balance each other out. Also, their relationship could be shown as a kind of unspoken alliance where they don't communicate much verbally but still know exactly what the other needs to do in a fight.
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.
Female Genos could be developed with a more empathetic side. Since she is a cyborg, she could struggle with understanding human emotions more deeply. Maybe she starts to learn about love and friendship in a different way compared to male Genos. For example, she might be more sensitive to the feelings of other female characters around her.
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.
Saitama would be shocked at first. He's used to Genos being around, always eager to learn from him. He might stand there in disbelief for a while.
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.
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.
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.
Their relationship could develop through shared experiences. For example, they could be on a mission together to save a city from a monster. During this, they face difficulties and rely on each other's strengths. Saitama's raw power and Genos' technological abilities combine well. This mutual dependence can be the first step in building a deeper connection.
In some fanfictions, his psychic powers are shown to have a much wider range. He can control more than just the usual objects. For example, he might be able to manipulate time on a small scale using his psychic powers.
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.
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.