Well, in the MHA manga, Dabi does meet his end. It's a poignant moment that has significant implications for the story's progression and the dynamics among the characters.
Killua is likely to be completely devastated. He might go into a state of shock at first, not believing that Gon is really gone. Then he could become very angry, either at himself for not being able to protect Gon or at the situation that led to Gon's death.
Sure, there are many fanfictions about Gon and Killua that might include a kiss. It depends on what kind of story you're looking for. If you like angsty stories, there could be ones where the kiss is a result of some big conflict or misunderstanding between them. Or if you prefer fluff, there will be those where the kiss is just a sweet moment in their innocent relationship. You can try searching on popular fanfic platforms and see what you come up with.
One popular theme is their friendship. Their bond is very strong in the original work, and fanfics often expand on it, like how they rely on each other in dangerous situations. Another theme is adventure. Since they are both on a journey in the original story, fanfics may create new adventures for them, such as exploring uncharted lands.
One common theme is the exploration of their deep friendship evolving into romantic feelings. Often, it's about the moment when they realize their connection is more than just friendship. Another theme could be about them overcoming some external obstacle together, and the kiss is a celebration of that victory.
There are quite a few out there. Some might focus on a moment of deep emotional connection between them that leads to the kiss. You can start by looking on fanfiction platforms like Archive of Our Own. Just search for 'Killua and Gon kiss' and browse through the results to find ones that have good ratings and reviews.
A very common theme is the exploration of unspoken emotions. In the original 'Hunter x Hunter' series, there are a lot of feelings between Killua and Gon that are not fully expressed. In fanfiction with a kiss, it's a way to finally let those emotions out. There can also be the theme of forbidden love in some cases, where they might face challenges or opposition to their relationship, and the kiss is a rebellious act against those constraints.
One theme that shows up a lot is sacrifice. Killua's willingness to sacrifice for Gon and vice versa is a big part of their relationship. In fanfictions, this can be magnified, with one sacrificing in a more extreme way for the other's well - being or for the sake of their relationship. Also, self - discovery is a theme. As they grow closer, they might discover new things about themselves and their feelings for each other.