Title:
I can see the connect in the description to the title which is good. I like how it says "will there only be echoes of love in the end?" because it kind of hints that there will be either a good ending or a not-so-good ending. I think 'Echoes of Love' is a pretty good title because it does have a hint of uniqueness and I think that's pretty important when making a title. Making a good title is hard but connecting it to the story can sometimes be even harder so I think that was executed nicely.

Description/Foreword:
The first thing I really noticed is the fact that the foreword is quite lengthy. I do think that shorter and to the point descriptions are the better ones because they leave the reader wanting to read more. I feel like the foreword could be removed possibly. The description can be left as is but I do feel as if the foreword is overdoing it for just the front page. Also, the change in font size is odd, I would try not to do that - using two different sizes, I mean. For the foreword, I'd put your author note/credits and trailer there instead of cramming them into different spots. I feel like the description should be used for story related things and the foreword is there mainly for things such as trailers, a/n's, other posters, credits, etc.

Also, this is something I say a lot, the character profile things aren't needed nor should they be used. You wouldn't open a book and find the list of characters there, they're usually introduced and described within the story. Plus, the little "character" section that AFF places there for a reason tells you who the characters are so it's practically just taking up space to throw them in there. The quotes don't really seem like they matter, the ones under the character pictures, so it wouldn't really be a crime to remove that mess.

Moving on to the description itself, there's a few things that do sound a bit strange. I took the whole description and will change whatever I see fit for change. Changes are mainly in red.

Given: No matter how long it will take, but the day will come when the world will smile at someone and now it’s my turn, Oh Li Na.
I think the better way to word this would be: No matter how long it will take, the day will come when the world will smile at me, Oh Li Na.

The reason I changed it is because the world is obviously going to 'smile' at the main character. The word 'but' really makes the sentence sound choppy in the original sentence. Also, the story is in first point of view, hence the 'I' and 'me' and it starts off as kind of third point of view. The way I put it makes it flow easier and it doesn't sound as choppy.

Given: After so much suffering, I finally got to know the good side of having the privilege of living and experience several emotions with my friends.
Correction: After so much suffering, I finally got to experience the good side of having the privilege to life while experiencing several emotions with my friends.

The reason for this change is mainly because you usually experience good things, like the privilege to living. I do think that "the privilege to life" sounds much better than "privilege to living" for several different reasons and the word 'experience' is supposed to be 'experiencing' either way. 

> I finally got to know the true meaning of the word love when I met Park Chanyeol, the giant of my class. However, fate decided that I had already lived experienced enough happy moments and decided to bring the problems back into my life.

The only thing with this one is that I would change lived to experienced since again, you experience happy moments.

Given: Now I have to solve the love problems of all which are indirectly linked to me. Will I be able to solve all the problems of everyone or will there only be echoes of love in the end? 
Correction: Now I have to solve all of the love problems that are indirectly linked to me. Will I be able to solve everyone's problems or will there only be the echoes of love in the end?

I had to take a bit of a take two on the last part because some things were very oddly placed. "Of all which are indirectly linked to me" sounds kind of strange which is why I changed it around. Also "all the problems of everyone" is grammatically incorrect in this usage because if you really read it, it doesn't make much sense. I get what you're trying to say in this sense but it just sounds strange.

As for the foreword, I won't correct much of that since I do think it can be removed as the description is perfectly fine on it's own.

Plot:
The description made me think this story was going to be completely different; I wasn't really expecting her to be a 'temporary toy' at one point so that's something I found odd. I mean, it does give me as surprise since I really just figured it was going to be a regular school AU thing. I didn't really take the time to fully read the foreword either since, as I said, is something that could probably be removed. It does give a nice surprise while reading the story instead of it just being out there that she was 'sold'. It's not a bad plot idea, I think there's a lot that can be done with a plot like this to be honest.

*Writing Style/Flow:
So, you wanted me to focus on this section and there's definitely a few corrections that can be made to the grammar. Like in the first sentence.

Given: I felt the huge car, which I was forced to enter, to stop in front of a huge house and the desire to cry increased even more.
Correction: I felt the car that I was forced to enter stop in front of a huge house and the desire to cry increased each second.

The reason I changed and removed some words is because there's no need to really emphasis the size of the car and if you do, I would explain the car more in general. What does it look like on the inside? What does the driver really look like (face. hair color, hair style, outfit)? The word huge used in the same sentence twice makes it sound kind of funny. I changed 'even more' to 'each second' mainly because it sounds nicer.

Also, the way the dialogue is executed with a - instead of the usual " kind of threw me for a loop for a second for two. I'm used to people using ' or " (though " is the more proper one to use) so that I found a bit strange.

I'm guessing the bold letters are her inner thoughts since she only talks when highly necessary.

When Jongin and his mother were talking, there were a few noticeable mistakes in the sentences.

Given: -No but. You know her better tomorrow.[...]- 
Correction: "No buts, you will be able to get to know her better tomorrow[...]"

The sentence was pretty vague since it doesn't really specify if he will be able to get to knew her better, it just says "you know her better tomorrow" which is just kind of odd. As for the word 'but', in this stance it does need an 's' on the end or it will sound weird.

Overall for this section, there is a bit of weird placement of words at times, forgetting of letters at the end of words (like but to buts), and some things sound a bit strange in general. It's not bad to the point of it being bothersome, hell I feel like most people wouldn't notice but as I am a reviewer purposefully looking out for these things, I do notice them.

As for the flow of the story, I think it flows pretty well - it's not terribly fast paced or agonizingly slow so that it a definite bonus.

Characterization:
I like how clueless she seems to the outside world. It really emphasizes the fact that she hasn't seen much of the outside world and that everything, no matter how small or normal it seems, amazes her because she doesn't really understand. Like her and the hot water; she seemed amazed at that fact and I really think it brings out her character.

Personal Enjoyment:
Since I really only read one pairing, this obviously isn't for me (as I'm not a fan of anything OC x idol) but it has it's potential. I tried to focus mainly on the writing compared to everything else which is mainly why the sections aren't all very long compared to the writing section. If I took the time to correct everything, this woulda taken a lot longer which is why I didn't but as I said, if you still want me as a beta I'm all for it.

If I forgot to say something, I wouldn't be surprised because I am so scatterbrained trying to do homework and such but I think I covered most of what I wanted to say.