I did have a thought. I have presented quite a bit about how I might do things, but how about looking at the work of a writer I consider FAR better than myself?
They asked Amber to become a magical girl three times. She refused. That only made her more interesting. The fourth time, she asked them.
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This thing manages to achieve a LOT with a little. Part of the secret here in what
@RavensDagger is doing is that between his' cover, title, and synopsis, the three are actually covering for each other and working in synergy. It is also working off of pop culture to supplement even more information.
The synopsis establishes we are working with magical girls. Anyone dealing with magical girl content in the modern day simply can't help but think of Madoka Magica, which had a heavy theme of time-travel. The story has "loop" in the name. This association is all you need to get in your head that there's going to be something time-travel related.
Finally, they synopsis gives an in-world perspective from a POV that would require you to know a thing or two about some characters in the story, namely the "cute creature" that gives the magical girls their powers. If you have read the story, it makes perfect sense that you are talking from the perspective of someone talking about the "cute creature" here.
This packs in even more information into fewer words. Also, it does not answer every question, and is a little trollish. Not a single word of that synopsis is inaccurate, but taking all the little snippets of information you gather together from these little details, it will lead you down some very wrong paths as to what actually goes on. However, that doesn't matter. It did not actually lie to you, and the fake plot you probably imagined in your mind was likely interesting enough to get you reading.
These are some really high-level writing techniques
@RavensDagger is using to get across a lot more information with fewer words. The cover art is also playing into the theme of giving fairly little information up front, but packing in a LOT of meaning that all becomes relevant and something you can analyze and parse apart as you start to read it. However, even when you haven't got any information yet, the bright red color of that circle drawn around the MC's face in the picture manages to pull this little mind-trick.
"Loop? And there's a circle there."
Every last detail about the synergy between these 3 aspects plays little tricks on the subconscious of the person viewing it. On first glance, it manages to use a lot of aspects of forced perspective to guide the prospective reader's thoughts in such a way that they really don't care about the fact they are not given much information, they are still interested.
A large part of this trick actually IS the fact that there is a lot of withheld hidden meaning to all of it that you have to read the story in order to understand. Your brain can sense those unresolved gaps in information, and it doesn't like it. It wants those answers, so you want more information so you can fill in those gaps. This is especially true when you can already almost answer a lot of those questions just by analyzing what's given to you without reading it in the first place.
A lot of the unfilled information also comes from outside sources. The cover art is designed like a personal add you put up on a bulletin board. The title uses the word "Agartha," which is a name for an underground city in Western Esotericism. (Have you ever heard the word "esoteric?" Well, the religion called "Western Esotericism" is where the word came from.) So, that's more borrowing from outside sources that adds to the itch in your brain. And, of course there is the Madoka Magica link it makes with the synopsis.
I could do deep into analyzing any of the three aspects there, but unearthing the reasons behind what it is not the point. The point is the very fact I'm ABLE to unearth this much information from so little in the first place without having ever read the story, and still have every single last scrap of information presented as well as information derived all be relevant to the story. That's the true mastery of what's going on and why it makes for such an effective synergy between the three.
