Yes, there are quite a few. You can start by looking on popular fanfiction websites. Some might focus on their relationship dynamics in the context of the original story's world, exploring how their different personalities interact.
Well, it could be a number of things. Maybe she faces some challenges, has a major life change, or discovers a hidden truth. But without reading the specific novel, it's hard to say for sure.
In Fairy Tail fanfic, the power hierarchy among dragon, demon and god can be really complex. Dragons are often depicted as extremely powerful with their physical strength and unique magic. Demons might possess dark and insidious powers. Gods could have divine and overarching abilities. However, it really depends on how the author of the fanfic portrays them.
Another option is Tumblr. There are often fanfic writers who post their works there, and you might be able to find some Himeno x Denji fanfiction by searching relevant tags or following the right blogs.
I haven't read this specific fanfiction, but usually, in fanfictions about Himeno and Hayate kissing in Pretear, it might explore their relationship deeper. It could be a sweet moment of their romantic connection, perhaps a turning point in their story where their feelings are more openly expressed.
In a fanfic, Naruto might power up by having a spiritual awakening. He could connect with the spirits of past Hokages in a deeper way, gaining their knowledge and some of their power. This could enhance his existing jutsu and give him new abilities. Vegeta could power up if he were to face a near - death experience against Naruto. This could trigger a hidden potential within him, like a new type of Super Saiyan form that has unique abilities. He could also fuse with another Saiyan (if there were another Saiyan available in the fanfic's scenario) to create an even more powerful being.