Mainly, Ash is a central figure as he is in the Pokémon anime. He's the one whose actions and relationships are often focused on. Misty, his long - time friend and now the one involved in the kiss with him, is also a main character. And Paul, who has his own way of doing things in the Pokémon - training world. His leaving after Ash and Misty's kiss is what makes him an important part of this fanfic.
One possible plot could be that Ash and Misty share a kiss, which is witnessed by Paul. Paul, feeling out of place or perhaps jealous, decides to leave. After Paul leaves, Ash and Misty might have to deal with the aftermath of their kiss. They could face mixed reactions from their friends, and they themselves might be confused about their feelings towards each other. Maybe they start to explore a romantic relationship further.
There are many fanfics out there that involve Ash, Misty, and the idea of a kiss, along with Paul. Some fanfics might focus on Ash and Misty's relationship development over time, with Paul being a rival or a side character that adds some drama. For example, in some fanfics, Paul's presence might make Ash realize his true feelings for Misty, leading to a romantic kiss scene. These fanfics can be found on various fanfiction websites.
It depends on the direction the fanfic writer wants to take. If the fanfic is more about friendship and Pokemon battles, then he might not. But if it has a strong romantic sub - plot, he probably will. For example, if the story is building towards a resolution where Ash realizes his true feelings for Misty, a kiss could be a natural conclusion to that arc.
One common theme is growth. Ash and Misty have grown throughout their journey, and the kiss in these fanfics can represent a milestone in their personal and relationship growth. Also, the theme of discovery is there. Discovering their true feelings for each other through the kiss. For example, in some fanfics, Ash realizes how much Misty means to him after that first kiss.
One good fanfic could be 'The Unspoken Feelings' which beautifully portrays Ash and Misty's relationship with Paul as an interfering factor at times. It has a great build - up to their kiss scene. Another one is 'Rivalry and Romance' where Paul's rivalry with Ash is intertwined with Ash and Misty's budding romance, leading to a very emotional kiss. You can find these on popular fanfiction platforms like FanFiction.net.
Maybe the author wants to build up the tension. In many fanfics, delaying the first kiss can create a sense of anticipation. Ash might be focused on other things like his Pokemon training and adventures, so his romantic relationships take a backseat for now.
I'm not very familiar with this specific 'pokeshipping fanfic' about Ash and Paul's first kiss. However, in fanfics, such a plot might be a creative exploration of the relationship between the two characters. It could be an attempt by the author to add a new dimension to their interaction that may not be present in the original series.
It's doubtful that it's a popular fanfic. Popular fanfics usually tend to build on the positive aspects of the source material, like the friendship or adventure between characters. A concept where Ash kills Misty is so out of the ordinary and negative that it probably doesn't appeal to a wide audience. However, there might be a small niche of readers who are interested in very dark and alternative fanfics, but overall it's not likely to be popular.
In some fanfics, Misty might be portrayed as betraying Ash for power. For example, if there is a powerful trainer who offers Misty a chance to become an even greater trainer, but at the cost of leaving Ash behind. She could be tempted by the allure of advanced training techniques or rare Pokémon that this new opportunity presents.