Perhaps there could be a fanfiction where a lemon - loving alien visits Earth and befriends Genos and Saitama. The alien brings with it a powerful lemon - based energy source that attracts villains. Genos and Saitama then have to protect the alien and the energy source from the bad guys. In the process, they discover new ways to use their powers in combination with the lemon - based energy, leading to some really cool fight scenes and a deeper bond between them.
One idea could be a story where Genos accidentally discovers Saitama's secret love for lemon-flavored things and decides to surprise him with a lemon - themed day. He could make lemon pies, lemonade, and decorate their place with lemon - scented items. Another plot could involve a lemon - related challenge where they both have to complete tasks involving lemons to gain some sort of power - up or reward. Maybe a mysterious lemon - themed villain appears and they have to defeat it using their combined strength and the unique properties of lemons.
The lemon aspect could be incorporated as a shared interest. For example, they could go on lemon - picking outings together. Saitama might show Genos his favorite lemon trees, and Genos could learn how to pick the ripest lemons. This simple activity can strengthen their bond.
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.
One idea could be that Saitama and Tatsumaki are forced to team up for a special mission. During this mission, Tatsumaki starts to see Saitama's hidden strength and unique charm, which gradually changes her initial dismissive attitude towards him.
One idea could be to have Genos from One Punch Man cross over with an immortal character from another series. Maybe they could team up to fight a powerful, otherworldly threat that neither could handle alone. The contrast between Genos' robotic nature and the immortal's long - lived experience would create interesting dynamics.
One common theme is the exploration of an unlikely relationship. Since Saitama is very powerful and Genos is his disciple, in a female Genos x Saitama scenario, it often involves how they navigate their feelings while maintaining their roles in the hero - disciple dynamic.
Another great crossover would be with One Piece. Saitama could be on a journey with the Straw Hat Pirates. His super strength would come in handy during battles against the various pirates and marines they face. And his comical personality would contrast well with the wacky and diverse personalities of the Straw Hat crew.
A cool plot might be a time - travel fanfiction. Saitama travels back in time to when he was just starting to become strong. He meets his past self and tries to guide him, but also has to deal with monsters from that era who are now different threats due to the time shift. And there could be a mystery element where Saitama has to figure out why time is acting strangely in the first place.
One idea could be Saitama and Tatsumaki teaming up to face a new, extremely powerful villain that even Saitama has trouble with at first. Maybe this villain has the ability to manipulate reality in a way that nullifies Saitama's strength for a short time, and Tatsumaki has to use her psychic powers to protect Saitama while he figures out a way to overcome this new obstacle.
One idea could be Saitama facing an enemy that can copy his strength but not his speed. This would create a unique dynamic as Saitama has to use his wits more than just his punch. Another plot could involve Saitama traveling to a different dimension where his power is nullified and he has to start from scratch to regain his strength. And perhaps a plot where Saitama has to train a new hero who is having trouble controlling their own power, similar to how he was once a regular person trying to become strong.
Adventure is also a popular theme. They go on quests together, facing various challenges and villains. It adds an exciting element to the fanfic. Additionally, the theme of acceptance can be seen. Saitama accepts the female Genos for who she is, and she in turn accepts his quirks. This mutual acceptance forms the foundation of their relationship in many of these stories.