One common theme is the exploration of their friendship turning into something more. The story often shows how their bond deepens over time until it reaches a point where a kiss is a natural progression. Another theme could be the influence of the volleyball team on their relationship. Maybe they support each other during tough practices and that closeness leads to the kiss.
Yes, there are quite a few. You can start by looking on popular fanfiction websites like Archive of Our Own. There, you'll find a variety of stories exploring different scenarios between Hinata and Yachi. Some might focus on a slow - burn relationship leading up to the kiss, while others could be more of a spur - of - the - moment kind of thing.
One common theme is friendship. Their initial friendship forms the basis of many fanfics. For example, in some fanfics, they start as just friends but then develop a deeper bond as they support each other through tough times.
Growth is also a prevalent theme. Both Hinata and Yachi grow as individuals in the series, and in fanfiction, their relationship is often part of that growth journey. For example, they might help each other overcome insecurities and become better versions of themselves.
There is a fanfic titled 'The Bond of Hinata and Yachi'. In this fanfic, it focuses on how they help each other grow, both on and off the court. Their shared experiences are written in a very heartwarming way.
There's also 'Hinata and Yachi's New Beginnings'. This fanfic focuses on their friendship evolving into something more. It has some really cute moments where they support each other during tough volleyball matches.
One great 'Haikyuu Yachi Fanfiction' is 'Yachi's Growth'. It shows her journey of becoming more confident in the Karasuno team. Another is 'Yachi and the Volleyball World', which dives into how she experiences the intense volleyball matches from her unique perspective. And 'Yachi's Hidden Talents' is also a good read, exploring some skills of Yachi that we don't get to see much in the original anime.
One common theme is friendship development. Since they are both characters in the same story, their friendship is often explored in depth, like how they support each other through tough times. Another theme could be the discovery of new feelings. For example, they might start to realize they have more than just friendly feelings for each other.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of 'Haikyuu' fanfictions, including many focused on Yachi. Another option is FanFiction.net, which also has a decent number of 'Haikyuu Yachi' stories.