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.
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.
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.
Asa and Denji found themselves in a strange new world. Asa was initially cautious around Denji, but as they faced various challenges together, like fighting off some odd creatures. They began to understand each other better. Denji's straightforwardness and Asa's determination complemented each other. Eventually, they became good friends, and their adventures continued, with each day bringing new surprises and a stronger bond between them.