One common theme could be adventure. Since Inosuke is a rather wild and adventurous character, fanfics might involve him and AOI going on some sort of exciting journey together, perhaps exploring a new and dangerous area.
Some other platforms like Wattpad might also have such fanfics. However, the quality can vary. You could also check out some anime - related forums. Sometimes fans share their own written fanfics or recommend ones they've read. Keep in mind to respect the rules of each platform when looking for these fanfics.
One possible scenario could be that Oga and Aoi's kiss was a moment of sudden realization of their feelings for each other. Maybe they were in a beautiful garden, surrounded by blooming flowers. The sun was setting, casting a warm glow. Oga, who had been secretly in love with Aoi for a long time, finally mustered the courage to lean in and kiss her. Aoi, initially surprised, then melted into the kiss, feeling all the unspoken emotions between them.
It could start with them being friends for a long time. Oga always had a soft spot for Aoi, but was too shy to show it. One day, they were at a school event, like a dance. Aoi looked so beautiful that Oga couldn't resist the urge anymore and kissed her.