So, here is the deal. The first chapters are the most crucial when trying to reel in readers. But when you are setting up the story, the first act that is, it can honestly be too boring to continue reading (especially when your protag is a high schooler). So I decided to foreshadow the dramatic question with a prologue, to make it more interesting. However, I'd really want the dramatic question be kind of a shock, both to readers and the MC, so the prologue will pretty much ruin that. A second option could be to make the first act super short and have the question hit the readers like a train. But a short first act would really leave the MC underdeveloped, though I might be able to pick up the characterization afterwards. The final option would be to just trust that my MC and the setting are interesting enough to carry the readers through the first act. So shoud I sacrifice the shock value to foreshadowing or risk losing impatient readers? Or are there some special factors I need to account for? (I also hope that I used the terminology correctly.)
Why would you try to foreshadow the major event before you have entered the story and begun to introduce the reader to the characters? Begin in the story. The readers don't need "preliminaries", even if it means they begin the story a bit off balance. It's far better to have the reader beginning with questions rather than with answers they have no questions for yet.
Don't spend chapter after chapter setting up the story before it starts. Start where the actual story begins, the inciting incident and you won't risk boring the readers.
Lumi, feed the shock as soon as possible. Analyze what the reader needs to know for the shock to make sense. However, you could decide to present it as a mystery, intriguing the reader to read on to find out what the heck happened....
Trust the reader. Your main character is going to be devleoped/grow throughout the story. Limit to what is absolutely necessary and allow the reader to know the character through the context of the story's events/plot. Find novels out there similar to yours you're working on. Study them, in this case the early chapters, and see how those authors accomplished it. Then apply to your story and your writing style.
Character development can happen during the action parts of stories. You don't need a long exposition to show the readers what the character is like. What I do is start my books during a very action-heavy scene, bring the levels down a little after the second chapter, and then let the natural flow of the story take over.