One common theme is friendship development. It could show how their relationship evolves from acquaintances to really good friends. Another theme might be adventure, where they go on some sort of journey together.
You can try looking on fanfiction websites like Archive of Our Own (AO3). There are often a lot of works related to different pairings there. Just use the search function and type in 'igarashi x nanashima' to find relevant fanfictions.
Nanashima could be the type to take risks in the relationship. He might be the one to initiate the first move, like asking Igarashi out on a date. Igarashi, though, would be the one to think things through carefully. He might worry about how their relationship would affect their school life and friendships, but eventually give in to his feelings for Nanashima.
One possible plotline could be that Nanashima and Igarashi start off as friends but gradually realize their feelings for each other. Maybe they go on a school trip together and have some special moments that make them see each other in a new light.
One popular nana x igarashi fanfic is 'Our Unspoken Bond' which beautifully explores their relationship through a series of heart - warming encounters. It delves into how they support each other during difficult times in their lives.
One common theme is the exploration of unrequited love. Often, either Nana or Igarashi might be pining for the other while thinking their feelings are not reciprocated. This creates a lot of tension and drama in the fanfics.
One popular 'kiss him not me nana x igarashi fanfic' could be 'A Chance Encounter'. It focuses on the unique relationship between Nana and Igarashi, with some really sweet and awkward moments that are very true to their characters in the original work.
They could start a secret project together, like creating a hidden garden on school grounds. As they work on it in secrecy, they share secrets and dreams, which deepens their bond.
Well, it depends on how you interpret the scenes. Some might consider it a kiss, while others might not. But if you go by the traditional definition, then yes, Nanashima kisses Serinuma.