I'm not sure specifically as I haven't read this light novel. It could potentially be about a character (hiraheishi) who dreams of the past (kako). But without more information, it's hard to say for sure.
One theme might be personal growth. In the fanfiction, Haru and Kazu could be depicted as growing as individuals and as a pair. For example, Haru might overcome his shyness with Kazu's help, or Kazu might become more patient. Also, the theme of teamwork can be prominent, as they are part of a cheerleading team. They might learn to work better together and rely on each other's strengths to achieve their goals in the fictional stories.
You can try looking on fanfiction platforms like Archive of Our Own (AO3) or FanFiction.net. These sites usually have a wide range of fan - made stories, including ones about Cheer Danshi Haru x Kazu.
It's difficult to determine the exact target audience without reading it. But if it has a complex plot about the past like the title implies, it might be aimed at an older teen or young adult audience who enjoy thought - provoking stories.
As I haven't had the chance to read this web novel, it's difficult to name the main characters accurately. But from the title, it seems that the central figure is the hiraheishi. There might be other characters that are part of the hiraheishi's past that start to appear in their dreams. It could also be that there are contemporaries of the hiraheishi who get involved in the story because of the strange dreams. For example, a friend or a family member who notices the hiraheishi's changed behavior due to the dreams and then gets drawn into the mystery of the past that the dreams are revealing.
The 'Something Ends, Something Begins' concept is deeply connected to the character development in the story. As Geralt faces different challenges, he often has to let go of old beliefs...
One common approach is to modernize certain aspects. For example, in modern adaptations of classic novels like 'Pride and Prejudice', they might add a more contemporary feel to the dialogue...